Hmmmm, I built motor using Loctite 242 on just about every bolt but did not use RTV on the bolt in question. FSM clearly identifies bolt to which you refer as having a coat of sealant in illustration. I'm fairly certain I missed this when I assembled engine.

By Joe! my bet is now on Kewlynx as identifing source of my problem... namely, pilot error! Ole Buck should pay closer attention!!!!