If you are saying that you filled the intake plenum:
Well since an intake valve is always open somewhere, you would have filled at least one cylinder with water, and water gets through the ring gaps pretty easy. To make this test accurate, the rocker shafts would need to be backed-off. Or if you set it up right, maybe just one side.
But if you filled the stat housing, well then, you may have more than one leak-source. This minor one, and the major one that must have had something to do with the now-removed timing cover.I would be scrutinizing that puppy pretty closely.
