The cap on my master cylinder has a little plunger attached (a suppose for the fluid level indicator). It would seem to me that it should have another cap on top of it. What does the cap look like on your e30?
Here's some pics from Ebay ads - from realoem.com it looks like slightly different style caps were used in different years and June '88 was a switchover month (apparently from ATE to Girling). http://motors.shop.ebay.com/i.html?_from=R40&_trksid=m570.l2736&_nkw=bmw e30 brake reservoir cap
Thanks. I have studied the pics on RealOEM and the ones you sent (they are also posted at Pelican) but nothing looks exactly like what I have. Mine is an ATE. Anyone out there who can look at their E30 master cylinder? Logic tells me that if I can push on the plunger then there is not an airtight fit, so something might be missing.
I'm not sure it's an airtight seal anyway - I'll look at mine later when I get a chance (don't keep the car parked in the house next to the computer, y'know )
