[luvbowties]

...another possible issue: suppliers, at least some, offer a mc for 68 vettes using a 1-inch bore and a different part# for those using a 1 1/8-inch bore. Also, the ones for manual brakes look just like the ones for power brakes, altho' they have different part #'s. As others have mentioned, that 'leak-down' at stoplights sounds like a failing mc.
sam