Taken from a previous post of mine a while back:
"It seems revisions E, G and P require breather pipe with valve. Revisions N, L, K, F, C and R do not"
So, to determine which you are most likely to need, find your current rev in these two sequences and go for the latest one. ***this was from my own research so suggest you have a look into it further to confirm, i don't want to be responsible for anyone buying the wrong part