The collar you describe is the ball collar where the u-joint is located. There needs to be a pint of gear oil in there to keep the u joint happy.
The oil in the amount you describe is likely a rear main seal. There are many debates on how to perform its installation, but many leak oil.
or it might be a little of both, wipe it all down and check it after running it and see where its forming at. if its from the ball collar it will be gear oil and if its the rear main seal it will be motor oil. thats how i determined what was leaking on the 40 before i changed to an open drive line and at the time it was both.
