I replaced the spring seats and struts at the same time. If your car has over 100k it's a virtual certainty that at least one of the struts is shot.

If it's not shot if you don't replace the seat it will probably get shot shortly.

What I didn't do is replace replace the rear shock mounts and (TA-TA!) I had a shock come through to the rear floor about a year later.

I'd replace everything, and the Bilstein HDs have been just great!

-BTC

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

"A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools." -- Douglas Noel Adams (1952-2001)