Thanks for the great advice all. Spook's seal tool instructions ought to go in the FAQ (IMO). However, I had pretty much decided to go the other route and remove the seal carrier and cam bearing cap and install the seals from the back per Jim's advice.
But....
I took off the upper timing cover yesterday to take a closer look. Cam seal is definitely not leaking. Oil inside the lower timing cover. For some reason I decided to put the end of an open wrench on one of the seal carrier bolts (2 are visible with the upper cover off, but you can barely reach them). They were not even finger-tight!. Tightened them up somewhat (can't tighten them properly without removing lower timing cover). Then I took off the splash-pan under the engine and tried the oil pan bolts. Front 4 were also loose. Tightened these up. I guess this explains why I have been losing so much oil recently. Don't have a counterhold tool here this weekend so I can't proceed further till next week.
There is some background to this. Early Jan this year I had my local independant Volvo shop replace the timing belt & seals (too cold for to do this myself at home). 2 weeks later we relocated 900 miles away (so I can't take the car back to the shop and have them take care of the leak). Soon after, noticed a pool of oil gathering on the previously clean floor of my new garage where the Volvo is parked. Gradually got worse over the next couple of months (maybe a quart per 200 miles). So my guess is that they were hurrying to get the car back together in the shop, tightened the bolts up finger tight, and forgot to come back with the torque wrench and tighten them fully.
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Current: '95 945, 98k miles; '90 BMW 325i, 95k miles. Former Volvos, gone but not forgotten '85 245, 250k miles; '91 744T, 150k miles

I replaced the crank and intermediate seals in my 945 by removing the seal carrier and doing the job on the bench. Those seals were so stuck that I had to use a wooden dowel and a hammer to drive them out. They had hardened so much that they just shattered like glass when they came out. The engine had less than 100,000 miles. I'd bet the seals were original. Putting the carrier with the two new seals back on was a little fussy but not too bad. I think it took me two or three tries before I got it on without turning back a lip on a seal.

For the cam seal, I just took off the cam cover, the front cam bearing cap and then the R&R of the seal can be done with your fingers. Soooo easy!

I've gone over 10,000 miles now with no leaks.

I used pretty much the same method as described by 'spook' below. Replaced all three shaft seals and the timing cover gasket last month. No leaks after 1200 miles. Read the FAQ's on this website, they were very helpfull.

Bravo to spook for a very thorough description.

1994 940 B230FT 96K

Dear Kev,

Good p.m. and may this find you well. Just did this on a 90 760 B230F (166K Miles), with a nephew.

We proceeded as follows for the cam and intermediate shaft seals.
(a) Removed seals using generic seal puller tool
(b) Cleaned seal seat using acetone (methyl ethyl ketone, a chemical cousin of acetone also works) to remove all dirt, grit, oil varnish, and other contaminants.
(c) Prepped the seal by coating it - inside and out - with an emulsion of 10W30 motor oil and bearing grease
(d) Slid the seal along the shaft, until the seal lip was just at the seat entrance.
(e) Pressed the seal gently into the recess, using an inspection mirror to ensure that the seal was perpendicular to the shaft, and that the seal edge was not rolled or kinked.
(f) Pressed the seal home. As there were no ridges in the shaft, we seated the seal about 1/32-1/16" lower than the block face.

We proceeded as follows for the crank seal.
(a) - (d) as above
(e) As the crank seal is too large to seat with finger pressure, we improvised a tool. We cut a plastic mug, obtaining a plastic tube 2.75" in diameter.

To be able to exert pressure on the tube, we took an old saw blade, which has a 5/8" arbor hole (the diameter of the crank bolt). We put the plastic tube over the crankshaft, put the crank bolt through the saw blade, and then turned the crank bolt into the crankshaft.

We slowly took up the slack, until the edge of the plastic tube was pressed against the seal. Using an inspection mirror to make sure that the seal lips hadn't kinked or rolled, we used a wrench on the crank bolt, to press the seal home.

To make a seal-seating tube, try the following.
(a) Buy a 1' length of 2" Schedule 40 PVC Pipe (white PVC wastewater pipe). Some Home Depots will sell by the foot, others only a 10-foot length (costs $5).
(b) Buy an end cap and a coupling.
(c) Drill a 5/8" hole dead center in the end cap.
(d) Polish one end of the coupling with fine sand paper (220 grit) to remove any letters, sharp edges,etc.
(e) Cut a length of pipe, with the length determined as follows. Screw the crank bolt 1/4" into the crankshaft. Measure from the under-edge of the crank bolt head to the face of the block. Subtract 1/2". That is overall length of the crank seal seating tool. Push the end cap onto the length of pipe. Measure from the outer top of the end cap, to that point on the pipe, equal to the distance from the under-edge of the crank bolt head to the face of the block, less 1/2".Then subtract 3/4" (the distance that the coupling adds to the length of the pipe, when the coupling is fully seated onto the pipe). Cut the pipe squarely. Polish-off any burrs, seat the coupling - polished side outward - onto the end of the pipe. You now have a crank seal seating tool. There's no need to cement these pieces, as pressure on them will keep them together.

Once you've slid the seal along the crankshaft, so that it is positioned at the entrance to its recess, slide the tool over the crankshaft. Center the tool on the seal, so that the seal edge exposed around the circumference of the tool, is as uniform as possible.

Turn the crank bolt until it contacts the end cap. Then, take a wrench and sloooowwwwly turn the crank bolt, to start pressing the seal into its recess. Stop frequently and inspect the seal with a mirror, to make sure the lip hasn't kinked or rolled.

If it does, grip it with your fingers and ease it back, and try again.

As there were no ridges on the crankshaft, we seated the seal 1/32-1/16" below the block face. If there are ridges, then seat the seal a little deeper, so that the seal can work on a smoothe surface.

Hope this helps. Let us know, how it goes.

Yours faithfully,

spook

No special tools required; use a screwdriver or seal puller to remove 'em, and tap 'em back in with a hammer(evenly around the edges).
--
Jim McDonald

hi there when i changed the bottom seals i removed the seal carrier as suggested by some people here, and install seals into the carrier on the workbench, but you dont have to if you do you need another carrier gasket, when you remove the seals clean the shaft that the seal will ride on so the new seal wont leak. maybe install the new seals a little farther in than the old seal, if a groove has ben wore on the shaft. i just tapped them in lightly with a hammer but some use pipe of the same size as seal like a makeshift tool. just take your time and dont set a goal for time limit. good luck.