Hello I have just had this problem on my mk2, same symptoms, I took the rocker cover off cleaned it up cleaned the cap and most importantly the breather (do not think mine has ever been cleaned in its 127000mile history) then we went for a scary blast up the A1 and down some fast back roads got her lovley and warm got back home and no mayo just nice black oil...........
Try it yourself but for the love of god keep your eye on the temp gauge when you are flashing around if she starts to run excessivly hot or have massive temp fluctuations it`s best to get it checked out proffesionaly ..don`t cook ya engine1
all the best and i hope this does work out for you