Would it be worth it to rebuild a master cylinder or should I just buy new?

In either case, since this car will sit most of the time how do I preserve the seals?

Would changing to silicon brake fluid help preserve the life of the components?
Since Si fluid is incompatible with DOT, what solvent would you clean all the lines with?

Tanks
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MPergiel, Walker, MI

Rebuild or buy new? It depends. My experience is that if the cylinder bore is not perfect, dont bother rebuilding. And my experience with corrosion is that it seems to be a bigger problem in the area between the outer rubber seal and the piston seal. I coat that area with red rubber grease and hope for the best.
dean

Good question. A controversial topic. When I rebuilt my brake system on my P210 (1967), converted to front discs, about 10 years ago, I went with silicone based on what I read at the time. (Somehow I got the impression that the more a car sits for lengths of time, the better the silicone option is). Although I drove it to work today, it is not a *daily driver* so I thought silicone would be best. I had no trouble ever with the brakes throughout the last ~10 years until...

Several months ago, given that 10 years (15?) had passed since the brake overhaul, I thought it best to flush the fluid and replace, intending to replace again with silicone.
A lot of gunk came out and in the process the master cylinder went bad.

I replaced the master cylinder with a new one (at least the second new one I installed in the car) and, again based on current reading and knowledgable mechanic advice, this time I replaced with Ate racing fluid (non-silicone). I probably flushed the system 3 times over. As of this morning, all is good...

Point is - you'll find differing opinions on this, all from knowledgable people. Current consensus appears to favor non-silicone.

Best of luck

KaiS

Michael;

I have recently taken apart Calipers on my 122, which I rebuilt about 30 years ago, with new OE Pistons, after which they were in service, or at least in contact with DOT5 silicon brake fluid while parked most of that time. The Pistons and Caliper internals had plenty of accumulated rust particulate (from I expect the insides of the original steel hard lines), but there was ZERO rust on pistons or bore IDs, and all rubber (Seals and Dust Boots) were still in excellent (reusable!) condition! I attribute this impressive long-term result to the use of non-hygroscopic DOT5 fluid.

I will be rebuilding my Master Cyl as a part of a complete brake overhaul, and be replacing and flushing all new (non-corroding) KuNiFer hard lines and (non-occluding) teflon/SS lines, so I wont have the need to flush out non-compatible brake fluid, but when I first converted over to DOT5 fluid, I pushed one full Master reservoir through each corner (at least once), until it came out clean and without drops of dissimilar fluid, figuring that had "flushed" out all the old fluid.

This is first-hand experience, and no particular recommendation for you, but I think that addresses your questions, and I know where I stand based on this experience.

Cheers