I've had my 8 3/4" rear for over 25k miles. The center section was a used junkyard part. I replaced the vent screw with one direct from dealer.

In the past few weeks its developed a peculiar leak. I've noticed dots on the driveway in the morning when I back out. A moderate leak, a good sized dot every inch or so. After a couple feet it stops.

It appears to come from the fill screw, not the gasket. Why now, after thousands of miles? It was tight when I took it out. Put teflon on it, tightend it back up, same. Washed it down, cleaned it up well... turning the shaft by hand with tranny in neutral, not a drop. Drove it again, several times in and out of driveway, seems well.

When I took the screw out, the oil stank something fierce and was a pitch black. I know a little smell is normal and grey maybe, but this can't be right can it? What went in at the beginning was standard valvoline 80w90.

Commuted again the next day and sure enough the dots come back. The relief screw seems clean, I'll have to take it apart and inspect further to be sure. Seems seeping from fill hole. Could it be creating that much pressure in the first few feet of movment to overcome the relief valve? I don't know how the fill screw could be leaking that much, all of a sudden. Maybe theres a crack somewhere? The pinion seal appears dry.

Sounds like a crack, in the filler plug or around the tapped hole, also a clogged vent to allow pressure to build-up. Get out the carb cleaner and a bright light and look closely.
DD

or more like a leaking pinion seal.

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1973 dart swinger