I rebuilt the front right one on my E39 last fall. Once you've done one or seen it done it is really quite easy. The cause is usually a bit of rust on the piston just under the dust boot. Steel wool and some brake fluid will easily clean up the piston.
'99 E39 540iT
Last edited by MLue1; 03-12-2011 at 10:34 PM.
Reason: adding more info