I have a 98 S70T5 with 54K miles and a 95 850 with 63K miles. Both have
done well and the 98 is no worse or better then the 95 (in fact, I
am getting real good at replacing upper motor mounts). My 98 did
have some initial probelms but after year 2 it has done fine and
has not had any additional warranty work.

My neighbor purchased a used 98 S70 and they like it. Their initial
complaint was light bulbs burning out all the time but Volvo
addressed that with a recall campaign. They have had no other problems.

I would also say that my 98 has had fewer problmes then what I see reported
here for other 98s. So, take my experience as just one small data point.