Yes that would be it, the flame trap. Anyone know where to buy one? (checked 126fan and axel gerstl but haven't come across it, or maybe didn't notice it....) Just bought a new oil filler cap as the old one's seal wasn't as good as use to be, but the problem was more with the fact that the middle 'stick' piece (the shaft with the spring and washer) was wobbling around and was letting out a bit of oil from time to time.
Thanks for the help and picture [-/