I did a little measuring and the mould is 1.5 tall yet the handle screws are 1.12 long, that leaves .37 of space between top of screw and top of mould block. I decided to drill a small, #38, hole in the top of the blocks centered over the end of the handle screws. This would allow penetrant better access to the threads and I could attack them from both ends.
Turns out the holes in the blocks for the screws are drilled long and there is only about .12 of metal from end of hole to the mould surface.
These holes will be under the sprue plate in use so lead won't enter them. I could even drill them a little larger, tap, and put in a screw to be peeled in place then finished flush with mould surface. I will likely just leave them as they won't cause any issues.
I used a small Allen wrench to help wick the penetrant into the holes and get them well filled. Time will tell how this works out.