Since I am the worst search person even though I have an advanced degree in data base admin... I thought I'd detail my findings on my MC replacement. I haven't found it difficult but wanted to explain some possible challenges and outline the procedure I used
1.) I ordered the Centric MC from Rockauto for my 1967 230SL. Low and behold it is an ATE and it was the right one.
CENTRIC 13035001 (130.35001) Master Cylinder $ 158.89
2.) Figuring that the minor leak would be solved and there was no damage to the booster, I siphoned the reservoirs and unbolted the mc. I was right about the booster but didn't actually have all the parts I needed for a leak proof re-assembly. BTW once the reservoirs are drained with a turkey baster and siphon tube I had very little fluid drip out and it was easily managed with a couple of rags stuffed under the mc.
3.) the mc from RA came with the O ring for the mc to booster seal but NOT the O ring for the forward reservoir or the seal for the back reservoir.
I have now ordered the rear seal for $8 (and a new reservoir) from Vintage Euro Parts in Ca. I will use a standard O ring to replace the front O ring and hopefully it will all fit and be leak free.
4.) my guess after having torn it apart is that the leak was not in the mc itself but in the rear reservoir seal - the $8 part. It was gooey and disintegrated when I pulled it out and appeared to be the source of the fluid leak. :-(
5.) back at it - the parts finally arrived - i'm tempted to castigate the USPS but won't flog that dead horse. I love old cars because everything is a bit of an adventure. I fitted the new reservoir and gasket and noticed that the rear seal and rear reservoir wasn't seating solidly down on the the mc. note: use a tiny bit of silicone on the rubber grommet and it will press into the mc easily. I noticed that the new reservoir had flashing between the bowls so I cleaned that out with a box knife and tried again. It's seating down a little more but not completely - but I think it's good enough and will seal fine since it isn't under any pressure.
6.) I've decided, "while I'm in there", to replace the flexible lines with Bud's SS flex lines so I'm waiting for them now. Should have thought of this earlier......
7.) Buds took a couple of phone call reminders but the parts (braided SS hoses for all 4 corners) arrived a few days ago and they are installed and the brakes bled and working - short road test, to be followed by some more extensive driving in the next few days. The hoses are relatively easy since I have a lift. The LR would be easier with the fuel pump cover removed but not all that bad.
8.) Since I have a power bleeder I chose not to bench bleed the MC which turned out to be a mistake since the power bleeder chose to "not work". With the help of a friend I bled the MC and then all 4 corners - no leaks so far and the pedal feels very firm.
