A few days back there was some discussion about the lack of a check valve to retain some pressure in the rear drum brakes in the E12 master cylinder commonly used as a replacement for the tii unit. I checked into aftermarket valves that could be added in to the system, and found a Wilwood unit for about $25 that could work, but it would require some sort of fittings to get it in line, and of course uses SAE threads.
Fast forward to Saturday, when I was helping a friend do a CV on his 87 VW Golf. I was looking under the hood basically out of curiosity, and what did I see sticking out of the master cylinder but 2 objects that looked suspiciously like the Wilwood unit, in the lines running to the rear brakes. The threads looked like they'd fit the 02 M/C. I checked with the local VW dealer this morning, and these are in fact residual pressure valves, P/N 176 612 151. They cost about $50 each new. I got 2 from a junkyard for $25, and they do fit the BMW M/C (I checked on an old one I had lying around.) I'll be bending the line on my car and fitting the valve soon - I'll keep the list posted.