i dont use any lube in my tc4, as you staited the gears are self lubed. means that a anti friction compound in the gears them sell. like high graphtie content etc etc. i have never had a problem. i sumtimes put a small amount of graphite powder on the pinion and spur gear. help run smoother great stuff.
even this stuff that caterpillar make's callled dry lube. comes in a spray form goes on wet then dries out excellent stuff. cheers
just my 2 cents worth.