I had this problem MP iron block / MP alum. head combination with Fel Pros. I switched and used the Aruzza gaskets and silicone as added insurance. I think it was Ultra black, IIRC. could have been Ultra gray. The Right Stuff sets up too quick IMHO.This did stop the leaking.
Currently using Cometics with Hylomar on the drain-backs and water passages.
Mark

BTW Aruzza gaskets max @ 4.320.bore


1996 Ram 1500 Sport
1968 road runner
1952 Sears Allstate licensed, pump gas, Hemi 5.98 @ 115.73 1.33 60 ft. The best is yet to come. Painless Performance / Street RODDER magazine Top 100 for 2019