These guys are great:

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They have rebuilds in stock, or will rebuild yours.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

There are several different remote boosters for the early 111 cars. If you have 4 wheel drum brakes on a 220Sb and your chassis # is below 070637, you probably have a T50/24/1, which also has a different master. Changing over to disk brakes on that car would require a different subframe and rear end. You can eliminate the booster and loop the two booster lines together and have non-power brakes, which a lot of people do. The brakes work fine but there is more pedal effort required. That way if you ever came across a kit or good booster it would be no big deal to fix it. And a few inches of brake line would be less than $5.00.
I am in the same boat right now. The booster works but makes a clunking noise in the front half. There is no brake fluid leaking into the vacuum side and the brakes work great, but the clunk bugs me.