And my 1998 V70R with AWD was great. Of course, the bevel gear fluid needed changing and the vicous coupling cmplained at low speeds. Other than that, just normal Volvo FWD proglems.
Leaking oil??? From where? If the rear main was replaced and the oil separator was not, then probably an oil leak at the rear cam seal. And probably a leak in the turbo return seal. I solved a leak from the weep hole in the intercooler by drilling a 1 inch hole in the air guide under the car.
The bevel gear falling apart is usually due to neglect. The fluid does need to be changed every 50K miles, as does the tranny fluid in your S70.
If the car is maintained, the 1998 is a good car. The only deal is the AC evaporator, which is very expensive to replace.
If the price is right and you feel up to replacing the oil separator and the turbo drain seal...

Klaus
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The more I learn, the more I forget. So why learn?