What type of motor oil should I use

Id use Shell RotellaT. Seems to industry standard

 

First and foremost, if it's dripping out the drain plug you're threads are probably screwed on that hole. Not uncommon.

I've had good luck running Mystic and a little Lucas in old motors.... only problem being it's not readily available. Honestly, though it's a Chevy Vs. Ford argument and will come down to personal preference.

It'll all work so long as you keep up on the maintenance.

 

My 01 c15 has had Rotella t 1540 ran in it from day 1. Has 920 on the clock. Rods and mains looked new when they were rolled. I've been tempted to try Schaefer synthetic blend for easier winter starts and all the other pros I hear about it.

 

X2 on Chevy vs Ford. at 935k on a Cat, you're lookin at an inframe here real soon. for piece of mind, spend the $300 and have a dyno run performed and also pull an oil sample and send it into a lab (don't do it at Speedco or some other lube/oil change place as your results will be diluted from the previous persons results). all this will give you a good ides as to what's going on internally.
I have no preference on oil.... I have a Volvo D-12 with 1.2 on the clock, same original injectors, turbo, bearings...ect. I use Delvac, and change every 12-14k

 

Pick the bottle that looks the prettiest.

 

What rating does your Mystic have

 

I have thrown a gallon of synthetic oil during the winter for easier starts. Dont know if it matters. IMO just change it frequently.

 

Meets or exceeds if i remember right. Used it in an old Detroit S60 but that was years ago.

New ISX gets Delvac 15-40.

 

http://www.chevronlubricants.com/en_US/products/products/delo-400-le-15w-40.html#.VuA77-YYM7A