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I have owned this 1979 320i E21 race car for a few months and am preparing it for vintage racing. It was sitting unused for about 5 years before I acquired it. It appears as though the entire braking system was replaced not long before the car was parked so I am basically taking everything apart, cleaning it up and checking for pitting, etc., and reassembling as all parts are like new. The one thing that puzzles me is the Brake Pressure Regulator which appears to be fairly new as well, but it leaks out the little brass stem that sticks out the bottom of it. Sorry, but I don't know the technical term and cannot find anything on the internet or in manuals that explains how it works or whether the leak can be fixed. There was a rubber ring around a groove in this stem that protrudes from the bottom of the brass cylinder and in the groove is a small hole. The rubber ring had separated, exposing the hole. I don't know whether it is leaking because the rubber ring was supposed to be sealing the hole or whether the fact that it leaks, indicates that something inside has failed. The rubber ring did not appear as though it was substantial enough to withstand much pressure from the hole. If it is a matter of replacing the ring, it should not be a huge problem to find one that will fit, but if it is something inside that caused brake fluid to leak through the hole, I do not see how you could get the unit apart without a special tool of some sort. I would be grateful if anyone could enlighten me as to how to fix this problem, preferably without having to purchase a new one. Many thanks.

Never tried to take one of these apart, but I also never heard of them leaking. It may be better to replace it, perhaps just with another used example. They are used (and the same) on all E21 excluding the pre facelift 323i as far as I can see, so with a bit of luck sourcing one shouldn't be too difficult. Please note the model changed at the time of the facelift (Aug-Sep 79) so if your car is a pre facelift example, you better get one from a pre facelift example to make sure it fits just the same.

Thanks for responding. I decided to convert to the brake pressure regulator for the later model that just has line for the rear brakes going through the regulator. Works great.