[Guy]

Mystery solved. I was not dealing with clean threads in the oil pan, but the drain plug threads were clean. I believe the shop that changed my rear air bags last year, and also did an oil change, was not comfortable with the drain plug, and used some type of black Permatex type of material on the threads that has held in there for 6000 miles. After removing this goo, the plug now bottoms out and feels like it used to. I will monitor the plug, but though I have never been a fan of it, I have never had a drop of oil leak on the pan. Here are a few pictures of the plug. I am thinking that someone must have given it a few ugga duggas in the past, or is that not a 3/8 drive plug ?

Has anyone installed a Fumoto valve on their oil pan? 

Thank you all for your advice. It is much appreciated.