Is it possible to rebuild a brake booster ? Do they

I think it srange that no rebuilt parts are to be found. With the wide variety of parts available this is a gaping hole in the hobby!Some guys LIKE rebuilding thier own parts. Some guys dont trust another to get it right...
Strange is right , is the 1970-1972 340 booster MC different than the 318 booster MC with disc drum setup ? There are so many MC available , but non look exactly like the unit on my car , which is original .