Some time ago, I think it was Kaptain Holister, suggested using generic vacuum tube caps rather than the BMW originals.

That prompted me to search e-bay for 4mm vacuum caps and I found these from China.

http://www.ebay.co.uk/itm/151669877430?_trksid=p2060353.m2749.l2648&ssPageName=STRK%3AMEBIDX%3AIT

Being longer and parallel, they are much easier to get on and off the vacuum take off points on the throttle bodies than the original short rounded ones, particularly No 1 cylinder with a fairing fitted.

I recently found 2 originals that I had dropped at some time, lurking under the air filter casing. 




Being silicon rubber, they should be less prone to splitting with age than the BMW ones.

Paul.

Excellent!  Thanks for that.  Those little OEM caps have always been a PITA.

Yep, I've ordered mine. The originals look like they may have a split up the side, but feel like they will fall apart if I try to take them off to examine them.

My oems were cracked and split also.
The ones I bought off the shelf at my local SuperCheap Auto store turned out to be vinyl but they're doing the job ok. AU$7 for a box of 6

I thought the tops off the plastic coated coat hangers would do the job ok

But not the white ones.

WHITE ones!......where can I get some. 

Paul.