[basketcase]

Those bails hold those lids on pretty tight. They should take some effort to snap in place. The lid doesn't appear damaged, so if there is no defect in the seal and the top of the master cylinder machined area is not damaged, it shouldn't leak. Since it has leaked with 2 different lids, I'd take a good look at the casting. Do you have 4-wheel disc brakes? That master cylinder looks exactly like the one on my 81 Corvette. On the Corvette it is slightly high in the front. Also my booster on my truck is smaller than yours and sits level holding the master cylinder level. My booster is about the same diameter overall as the smaller diameter front section of yours and would probably clear the custom hood hinges you have.

Tom