I am pleased to learn that the WP on these motors is long lived. I am in the middle of changing out the TB on our 2002 S40. When we bought this car two years ago it had less than 25k on the clock--had been owned by a li'l ol' lady who had passed away three years previously. Before even starting the motor I pulled the TB top cover and examined the belt which looked to be in very good condition. Checking service intervals I found the recommendation to be 168 months---14 years! Now with just under 55k I checked again and found the back side of the belt to have very tiny spidery web cracks--obviously time to change it. I was concerned about the WP - which by miles, at least, was young but ordered one when purchasing the belt just in case.
My plan is to examine the original WP and check for these conditions---Does it rotate smoothly with no indication of a bad bearing?---and--does it have some resistance to rotating due to the seal still being tight? If those conditions are good I will probably leave it in place rather than install the aftermarket WP purchased. -- Dave