Master Cylinder Leak

[Lucky_Lou]

Ive developed a leak from the master cylinder its the round one 1980 there are two Allen screws holding the end assembly on where the pipe goes down to the front brakes there's an "O"ring seal which i replaced when rebuilding the bike i cannot see the point in replacing it again so i thought i would strip it and rebuild with some sealing gunk of some sort.......any suggestions
Lou

[weasel01]

It could be scored inside which would and require honing.

[nhmaf]

Unfortunately the round ones are not nearly so rebuidable-friendly as the rectangular ones.  Actually, aside from replacing the piston assembly, I don't think that BMW claimed that the round units were rebuildable, but you may have some luck.   Are you certain that the leak is coming from the plastic reservoir-to-alloy body interface?  If it is leaking past the seal(s) in the piston/chamber, the chamber itself may indeed be either scored or corroded and could require homing and re-sleeving to fix with standard parts.   alternatively, you may find a rectangular, right hand side perch assembly used that you could upgrade to.

I rebuilt the rectangular unit on my 82 R65LS a few years ago, and it worked fine for about 1-2 years, and then started misbehaving again, so I just bit the bullet and perchased a new M/C assembly.

[Lucky_Lou]

I cannot be sure if its the "o" ring or the interface between the plastic  reservoir and the metal a friend in the motor trade has offered me some liquid rubber for the interface i may try that first then strip the joint hone the surfaces and replace the "o" ring i was wondering if there is a jointing compound specifically for brake fluid?
As i recall the assembly costs an arm and a leg that would definitely be last resort.
Lou

[nhmaf]

They are not inexpensive, but I also think that the rectangular ones are less expensive than the older round ones, for whatever reason.   Still, I paid approximately $175 for a whole new rectangular M/C assembly a year or two ago.

[Lucky_Lou]

Am i right in thinking the rectangular ones are for the single throttle cable (with splitter) where as the round ones are twin cable??
Lou