Per this, page 2 axle breather info ref part 21H6060 and MIG Wielders photos:
viewtopic.php?f=4&t=32294&start=15
I removed mine and it is totally different. See pictures below. It's made of metal, has a much coarser thread and can only be removed using a spanner. While it may have once had a split pin down the middle it doesn't now and is essentially just a hole facing upwards from the axle. It wasn't clogged up so no issues with the breather as such..
Do you reckon I should just put it back on as is or does it need some type of cover or split-pin plug?
thks