I had to replace mine (201) last year. I had been experiencing a low pedal and clutch drag. I found the pushrod was worn about 1/8" at the contact point with the clutch fork. There was no external leakage or internal corrosion. I flush the fluid every two years.

The Haynes 190 manual was a good guide, and I think they make one for the 123. Access to the hydraulic line is very tight and required a wobbly extension with a crow foot tubing wrench of proper size. I think it was 12 mm, but can't remember for sure. I accessed the two mounting bolts (10 mm hex IIRC ) from behind with a couple of socket extensions. That's all there is to remove - the B-nut for the hydraulic line and the two mount bolts. Once I figured out the correct tools to get a bite on the nut and bolts it was quick and easy.

Another key is bleeding. Per the Haynes manual, I bled from the "bottom" up by connecting the RF caliper bleed valve to the slave bleed valve, which was open about a half turn. You then "bleed the brake", which forces fluid into the clutch slave cylinder and forces the air up and out to the reservoir. I did the clutch bleed after flushing the brakes, so it was fresh fluid. An empty clutch slave is almost impossible to fill/bleed by conventional bleeding at the clutch slave that you use for the bienniel fluid change.

After looking around for rebuild kits - with not too much luck - I bought a brand new slave from Fastlane. It was a Teves - only about forty bucks - and the cylinder has the MB casting number - same as the original.

Duke