Actually the rear main seal is not a huge concern, the AC evaporator is. Then there are about a bazillion little electrical things.

I was going to ask you why you don't just throw in a used 9000 motor, there are piles used engines and transmissions around for Volvos. But I didn't see a lot of 'em listed on e-bay for Saabs. What's with that?

-BTC

'98 V70 T5 5-speed, 167k mi, velour cloth seats, front IPD stabilizer bar, rear factory HD bar, Bilstein HD, Volvo strut tower brace and skidplate, e-codes, XC grill, Lidatek LE30, V-1, Mobil-1 since new

"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." -- Douglas Noel Adams (1952-2001)

There are two major expenses on the 850/70 models: AC evaporator leaking and the rear main seal.
The RMS starts leaking due to excess pressure inside the engine block, which is due to insufficient/improper maintenance to the PCV system. If there are no oil leaks when you buy an 850/70, you should be OK. But you will need to ensure the PCV system breaths correctly. Vacuum lines tend to harden with age and the elbows crack everywhere. There are kits to replace elbows, lines, and oil seperator box. The engine/tranny must be removed from the car to replace the RMS.
The AC evaporator leaking is a different story. Like the 240 heater boxes, it appears the car was built around the evaporator. Because the entire dash needs to be removed to replace the evaporator, expect a very large labor bill. Some of us are putting it off by adding R234a 2-3 times each summer. Adding one can in the spring and having it last all summer is very common.
Of course, a manual is preferred over an automatic, and the clutch is reputed to be worth 150K miles. But there are a lot of auto boxes still working very nicely at 250K. The fluid for an automatic should be flushed every 25K miles or so.
In 1999, Volvo eliminated the cable from the gas pedal to the throttle body. This allowed for failure of the ETM, a sudden loss of your gas pedal without warning. Visions of being stuck in a blizzard in Minot, ND, or rush hour on a LA freeway. The ETM is now warranted up to 200K miles. 1999-2001 models are effected.
Good luck in looking, Volvo still builds the best full size wagon.

Klaus
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(V♂LV♂s 1975 164, 1995 854T, 1998 V70R)