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I'm not thinking the the weight of the oil is the most likely cause of your problem.
Perhaps you are running the oil level too high.
Most it seems and I am one of them run the oil at the mid point between the L and F mark. Running all the way to the full mark can make oil leaks from the rear main worse. Also make sure your dip stick is going all the way in. Sometimes the double thickness of the wire loop end is not pushed all the way into the opening for the dip stick. Not getting it all the way in and running the oil to the full mark will definitely cause a leak.
A's for the most part drip some oil out of the rear main on shut down.

Check to make sure the breather cap on the tube for putting oil in isn't pushed down too far blocking free air flow through the tube into the engine.

There is a small inspection plate at the rear of the engine that can be removed to get a look inside the flywheel housing and you can see some of the rear main and the oil pan seal. Take it off and have a look with a bright flashlight. Look with the engine off and also while running.