Bill, I have a International 454D its about a 1972. The vent under the seat would normally not put out any oil unless it was to full or perhaps the cap and small filter device is not in place should your's have it like mine. The differential lock while it does not make noise will grind occasionally if your rolling and engage. If its locking up, it should be OK. I find that when I get stuck, engaging the diff lock rarely helps me get more traction. There have been occasions such as when I high lift one drive wheel but more often then not I'm in mud and I'm stuck. My F250 in 4WD is my 4WD for that tractor. Heavy solid tractor with a 3 cylinder diesel. Rat...