Right stuff is the only thing I've found to keep the pan and front cover dry, but you'll all but destroy them if you have to take them back off. PFS seems to work well for everything else.
Get some RT150 exhaust manifold gaskets for 12V's. They're 3 composite layers and 2 steel layers with a "fire ring" crimped in them. I've recently started using them, I think they'll be a respectable Band-Aid for questionable gasket surfaces. Stock up though, it took me 3 weeks to get the first 24 (on emergency order) , I've got 60 more on order.
I've been looking for that style gasket for 8.3's.
Herc's can be sealed up without much trouble. If you use a rear seal speedy sleeve from AGCO, it's too long and when you bolt the flywheel on it wads the sleeve up and the seal leaks. The rear main cap seals can also leak and appear to be a leaking rear seal.
Side note Chris, if you need crank seal drivers for the 6.7 RGT engines, I have a set. They'll make you pucker if you price them.