Hello Sig,
I agree with the guys, in that if you aren't smoking you must be leaking. If the vent tube is the culprit and you drive highway speeds, it would seem you might have a nice oily coating at the very least, all under your truck... that's a lot of oil loss to me.
I think checking the gasket seal areas is a good idea, again you'd have oily areas from the source, down.
Curious... do you have a vacuum fuel pump? I've read that sometimes gas can get dumped into the crank case.
I'm asking... guys, could gas mixed with the lube make the lube go away? I'm not a guru... but I think in checking out everything, I'd check this too.
At least you're on top of it and not ignoring the problem. Hopefully you'll have this mystery solved and put your mind at ease.
Please keep us posted... this is something many could learn from.
Jerry
