Okay, so I mentioned in my build thread (and elsewhere) that my XS650 arrived with a nasty, leaky, ugly master cylinder. I decided to do what I did with my Honda CB650, namely put on an aftermarket unit from a vendor I trust. When I posted my intentions on this forum, I received numerous suggestions to use a master cylinder with a smaller piston (14mm being stock, as I understand it). So I did. To be clear, the front brake basically didn't work when I got the bike. Putting on the aftermarket unit and bleeding the system resulted in me being able to lock up the front brake while rolling the bike around manually, but the brake doesn't have the positive, solid feel that I got from the replacement I put on the Honda. The lever does not come back to the grip, and I see no fluid leaking out anywhere (nor does the level seem to be going down in the reservoir). I bled the brakes a second time and got a few very tiny bubbles, but this made no change in the behavior of the brake; if I didn't have a really solid rear brake, I wouldn't dare ride the bike at all. It feels kind of squishy, honestly. There are several possibilities, of course. The replacement unit, a different model than I got for the Honda, might not be as good, or it might be defective. I don't see any sign of the latter, though; the only defect I can imagine in it would be if the piston leaked fluid back into the reservoir, but if it did that the lever would eventually touch the grip as it lost pressure. Secondly, the caliper could be bad somehow, though I don't know how; third, one or both of the original brake lines could be bad. I'm leaning that way, honestly, but I'd like some extra opinions before I buy any more parts.