How much gear lube to add?

[Pirate_Freder]

So I know Rawze explained this and he said that if you're engine is past 300k to just add a full gallon. I'm wondering how loose that is assuming the engine has become though. Seeing as the ISX doesn't do well with overly thick oil I certainly don't want to take it too far.

I have a 2010 KW 660 with a CM871 525hp with 318k. The main reason I am thinking I might want to go easy on the gear lube is because I only have 4.5" of blow-by, plus judging by the wheel horsepower it doesn't seem to have lost any. I'm not sure how correct they were but when I spoke to a Cummins shop about my dnyo/blow-by results their reaction was "Holy s#!*, that engine is like brand new". I'm leaning towards only half a gallon of Sta-Lube 85w90 in my Rotella-T dino 15w40. I would greatly appreciate some input on this as I am just going by my educated gut feeling.