had a customer years ago that had what he thought was a rear main leak on a 340. After several pan gaskets, rear main seals and a new oil pan he brought it to us. My first question was are you sure all the block plugs are tight. Swore they were. OK, we did the rear main and pan gasket again. No change.
Fortunately it was a stick so we dropped the inspection cover and brake cleaned the 💩 out of it. Fired the motor up let it run a few minutes and the leak appeared. Using a small wadded up paper towel on the end of flexible fingers i was able to sneak it up in the bell housing while avoiding the rear main area. When removed fresh oil was on the towel.
Pulled the trans & flywheel and found the right galley plug finger tight. 😳. it hasn't leaked a drop since in 15 years. he left a spare pan gasket and i had a buddy make a sign that "Said think outside the pan John"
LOL