The locating pins in the block had to be removed to 'deck' the surface. If the pin/pins bottom out, this could cause the gasket leak. The Fel-Pro compos gasket is a great design and the compression of the gasket is key to 'no-leaks'. The 'water glass' was a method used on a few of my Ford flathead cracked valve seats. It does work great on cracks and small leaks, but it can also restrict radiator and heater core passages. If you have no luck with some of the suggestions you have, I will suggest checking head and block surfaces.Check the locating pins.
