Dan:

I'd not bother to take a master cylinder apart unless I had a rebuild kit to put in it. There are only two reasons why a master cylinder will fail -- worn bore (scores, corrosion, etc), in which case it is junk, or bad piston seals, and you cannot fix those, only replace them.

Before you condem the master cylinder, check all the hoses -- front and rear. They can look fine and still leak internally, with the outer rubber swelling up when you step on the brakes. This will give you a mushy or sinking pedal, and hoses are MUCH cheaper than a master cylinder kit. I'm doing all of mine -- would hate to run into someone because I was cheap on the brakes!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!