he probably has a cheap cap , the genuine volvo one has a shiny lacquer inside to prevent this ...

Possibly, but it's likely the original cap as the car had only 25,000 Miles on it when he got it.

I've just remembered, my car also suffered the same problem when I first got i,t a clean and spray with WD40 seemed to clear it. I bought the car with over 150,000 Miles on it about 8 years ago, so I can't vouch for the originality of the cap, but it's given no further problem.

Ours is now wearing a Marigold rubber glove with the fingertips snipped off and ty wrapped to keep the moisture out. Looks kinky but I hope it works.

OUCH!!!!! :err: :lol: