Hi there,
Reading your thread with interest.
Had a quick look on eBay at the different ball joint options for this model and I can see that some are 21mm and others are 18mm.
what was interesting is that one of the listings for an 18mm ball joint says that it will only fit 2008 model V50 D5s with the last 6-digits of the chassis number up to "209290."
https://www.ebay.co.uk/itm/VOLVO-S40...EFp:rk:11:pf:0
Whilst on the subject, I'm looking at buying a V50 D5 of similar vintage and was interested to read your comments on overall reliability.
What sort of MPG are you getting on average and is that mostly urban stuff or motorway?
Also, is your car running standard power?
J