Audi TT buying - smoke from oil filler

[Tom217]

Hi, I’m looking at buying a convertible Audi TT mk1 for the summer. I went to look at a 2000 reg the 1.8 225hp today, when I checked under the oil filler and saw some slight foaming at the top, the seller told me the car has been sitting for a while and that it was a moisture build up (which is believable) after the engine had warmed up on idle I looked under the cap again and white smoke was coming out of the oil filler with a slight pulsing action. Is this normal for a 5 cylinder Audi? Or is this the piston rings failing. Any advice is appreciated.
Thanks,
Tom