As the refurbishing/renewing/restoration of my '70/4 continues, I began wondering about how long a brake master cylinder service life would be. I replaced the OEM 17mm w/a OEM 17mm in 1984 when the original started leaking. At that time, I also went completely through the pedal cluster, stripping and refinishing same and replacing the pedal bushings.

Now here it is 20+ years later, and the brakes have been fine and there is no m/c leaking problem. But 20 + years on the m/c? The brakes have been bled periodically and there are no pad/rotor/caliper issues here.

To replace the m/c or not? I'm inclined to do so, though others have said "why bother".

Just keep clean fluid in it and it could last a VERY long time.
Compete flush yearly minimum. I push fluid out monthly about 1/2 pint.

There are teeners running around with the stock 17mm M/C still working, mine

was when I replaced it and it was 30 yrs. old. But if your gut tells you to replace/

rebuild it then do it.

I've torn apart 37 year old brakes that look like new inside because... they got new fluid every year! I've torn apart some that have what I call "Caliper Worms" in there as well. This is when the fluid hardens and creates all sorts of problems.

To ease the process, get yourself a set of Speedbleeders.

Well worth the money, and you can do the bleeding by yourself with no hassles.

Back in the day, even with twice annual fluid replacement, we were lucky to get seven years service. I've replaced lots of MC's for customers.

Torsion bars and shocks were about the same.