MB brake systems are bullet proof for obvious reasons. The rebuilding process for calipers is really nothing more that replacing the O-ring inside the piston sleeve and the rubber collar that surrounds the sliding piston. with my 90 300E, I found that some corrosion had formed a ring around the piston causing both pistons from each side to stick so much that they would not move forward to engage the brake pad. (The previous owner, never changed the fluid it seems). I gently took the corrosion off with an abrasive pad and followed up with a fine steel wool to get the side as smooth as possible, replaced the O-ring and collar for both caliper for less than $25 (while at it, I went ahead and replaced the hoses, and cleaned up the caliper sliding surfaces). Now all is well again.

Good luck.

__________________
03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio