Did the job last night. There is no way I could have gotten the oil separator out without removing the intake manifold. And that is because of the way the wiring harness under the manifold is routed.
It was actually the easy way out, because I had room(not too much extra) to get it back in and be confident that it went in properly.
I did come up with a trick, which was to attach a "bungee-cord" to the throttle cable bracket, and the other end to the raised hood. This held the intake manifold up out-of-the-way without too much strain on wires or hoses. It was up high enough for me to be able to remove the oil separator, and deal with the removal/replacement of the intake manifold gasket(NAPA-$6-in stock).
I did feel the pain of buying the green o-ring for the oil separator at the dealer for $6. And the parts guy just hands it to me, not even in a bag.

Car is back together and starts. I am doubtful that this fixed my oil leak, since I did not find any real blockage in the entire system. I did change the seal on the oil cap also. I had one in my "Volvo Parts" shoebox which will need replenishment at my next FCP Groton order.

So tonight, it is back under the car to see if it is still leaking, and to take off the brace which hides the back of the oil pan. Is it OK to run the car with that off?

As always, I am grateful for all the advice and encouragement.

If your going to the trouble to do that, while not terribly hard, I would replace the Jetronic temp sender under there and the heater core hoses too, since there will never be a better time to do those. You won't have to disconnect the fuel line to unbolt the intake and move it over slightly or for that matter the throttle cables either. You will probably want to unbolt the two grounding wires though. Don't be shy, it's about as easy of a car to work on as you will find. Slow and deliberate is good, but shyness is not rewarded. ;) Do have a gasket on hand for the intake.
Charles

When I did mine (on an 89 240) I left the intake manifold in place. I had already removed the throttle body and idle stabilizer while fixing another problem, and noticed that the separator was leaking around where it meets the block. I unbolted it and there was just enough room to get it out. I cleaned it out and put it back on with a new O ring, and so far, no problems.

Be careful around the rubber hose that goes down into the oil pan (it's under the vapor separator, the top end of it looks like another O ring) It will be old, hard and brittle. If you are thinking about replacing it, that requires caution too, as the lower part of it can break off and fall down into the pan.

Auto Zone has the gasket in their catalog. Just log on, and you should be able to find a store with one. www.autozone.com

Good idea to remove the intake manifold to get at the oil separator. I think the '89 has the tall separator.

Haynes says 16 ft-lbs on the intake manifold. Not much. Aluminum head.

Scrape the mating surfaces smooth with plastic to get the old gasket off.

Have a new gasket on hand.
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1986 Volvo 245

I have the manifold off my 1991 740 right now to get to the oil seperator. While I don't have the torque spec on me for re-installation, I'm sure it must be in the faq somewhere. Also, I plan to hand-tighten the nuts first, then start torquing them in increments, starting at the middle and working my way outward to the ends. You need to be careful on that aluminum head. Fortunately it is studded.

If someone has better advice, we would definitely appreciate it.