help with 64 dart rearend

Clean everything as good as possible & when you see fluid leaking again see if it is running down from the pinion. I had a leak & thought it was the cover but it turned out to be the pinion seal. It is still a fairly easy fix, just unbolt the driveshaft, hold it up out of the way with a bungee cord, get a new seal & see about borrowing a puller from the local auto store to pull the pinion yoke off, replace the seal & put it all back together. There are lots of write ups on replacing pinion seals.