Actually, the rear main seal is a part that leaks on a lot of them (mine did around 80k miles). It's nothing huge. It cost about $400 to fix. The part was $25, and the rest was labor because you have to drop the tranny to get in there.

To be honest, i paid about $6200 for my V90 in 2005. You can probably find a better price if you look around and haggle. My friend just sold his 2002 s60 for $6000. Never underestimate the power of a volvo to depreciate.