Disc Brake "O" ring issue

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I know - this is a Corvette - but seems like there are many more self-fixit and knowledge guys here than on the Vette forums elsewhere and an old caliper design is just that.

I have not been able to take this vehicle out very often and keep it stored in a warm/dry/tight garage. One caliper wants to leak just a tiny bit when sitting for quite a while and will stop leaking if I drive it a bit. But, time to stop that.

The problem is a the upper fluid pass through site where an "O" ring is clamped when the two sides are tightened. I opened the caliper. Upper and lower "O" rings look good, but the slow leak site is evident.

A while back an outfit that installed stainless steel caliper linings kept my original parts and sent me another lined set with new key components. That is when this started.

Today, some edges of both housings look as though they had not been thoroughly machined and seemed a bit high in places on the outside edges, so I have carefully filed those edge surfaces as flat as my old eyes and hands can manage. Any interference there could have enabled enough clearance for the "O" ring to leak that tiny bit. That could be the solution.

But, I am also concerned that the inset on the face that holds the "O" ring may have been bored a bit too deeply, so when going to the city tomorrow I am going to try to find some "O" rings with the same ID and OD but a slightly thicker profile.

I cannot get a perfect caliper reading on these rubber rings, but the ID seems to be about .30 and the OD about .40, and might that not mean a thickness of about .10? But, the thickness measurement with the caliper seems to be about .060.

Am I likely to find an "O" ring of the same ID and OD with a thickness that measures more like .070 or .075? If I get some, would that be too much added thickness? Is there a grand source to see "O" ring sizes available? Or, should I try to install a very, very thin shim at the base of the "O" ring insert opening?

If those of you who know disc brakes well have any insight to offer on any aspect of this issue, my ears are open and appreciative.