That's really weird, because I just had similar problems with my front brake. Talk about karma, but all the things I suggested worked. My problem turned out to be the banjo bolt loosening causing a weep at the bolts. Re-tightening didn't work because the crush washer was worn out. I replace the washers with what I could find which turned out to be with a slightly smaller OD but same ID. Tried heaps of things, thought the hose might have been leaking. Just couldn't get the pressure back on. So I took it into a bike shop and they replaced the washers with some they had which were nearly twice as thick and alluminium (although that shouldn't matter) and just a bit bigger overall. Same ID though. He had to re-tighten it twice but got the right crush in the end. Seems to me like there is a bit of a trick to it. I know I couldn't get the right crush and I really tightended the crap out of it. Had the lever pulled in overnight on the side stand so the cylinder is definately the highest point and it's all back. Before I brought it in I also rode down the street to let the ABS kick in, and I'm confident that's enough. BMW here don't even open the ABS valves and don't know how to do it either.

I know it's frustrating, I fiddled all easter on it and got so fed up I let someone else do it on Tuesday. Sucks being defeated eh. I'll give it a good run this weekend.

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