Oil filler tube, part missing ?

[Chris Garner]

Martin, The part you are referring to is a conical mesh filter with fits into the filler tube, a little like an inverted witches hat. Rarely found in engines these days, I've only had one car with it fitted and it was in bad shape anyway. Designed purely as a filter, not to prevent upward splashing, although I suppose it would have prevented some I expect. I wouldn't worry about the splashes, all part of everything thrashing about below!
A cylindrical filter was also fitted in the petrol filler neck, I have one in my Top Hat. Useless really as with the force that modern pumps deliver fuel these days, if left in you end with fuel all over your boots...and everywhere else.