I think it is really a hit or miss on the seepage issue, all depends on how tight the JFC ring is in relation to the base machining.
I really don't think its how tight or loose anything is, the juice has to get past the oring first to get past the AFC or JFC to seep or leak. I still lean towards thin stock oring on the base not cutting it, but I've been known to be wrong and next step if the oring replacement don't work is hopefully not wrecking my merlin taking the base apart. So far so good...no seepage onto the 510 but its only been a few hours