Got a pair of used but good condition Master cylinders.

1st is a 19mm $120 $110 shipped
2nd is a 17mm $100 shipped
(CONUS)

(They have the line seals in them to retain the washers but should to be replaced)

Those look pretty clean. Repainted or OEM?

I just may be interested in the 17mm ...

Yes. Spruced up the Ext. from the the OE surface rust.

Can a MC be tested once it's out of the car ? Where do they typically leak ?

A lot of the time, they don't leak externally, the fluid passes by the seals (pistons) inside and doesn't pressurize the line(s) going to the slave cylinder(s) ... (caliper(s) in our case).

If you have a spare pedal cluster and a vice, they can be bench tested with a pressure gauge.

The crux of the failures is rust/corrosion in the main bore of the cylinder.
Once the bore becomes pitted the, wiping of the bore wall by the seal is compromised.
IIRC this is compounded by the two different metals used: the Plunger=Alum & the Cylinder itself=steel.

Its pretty easy to determine if this is a problem as a simple large snaplock/circlip holds the plunger in the bore once removed you can usually see if you have damage.

That's why it's recommended to replace your brake fluid every year (or other year). Brake fluid has the propensity to suck moisture out of the air somehow.

Hey Rich, I am your man for the 17mm MC. Send it to me please.

PM'd.

still available