While using my 6500 on Monday, the oil pressure dropped to 10 lbs. I went into town to buy an oil pressure gauge. I wanted to make sure it wasn't the oil pump. I stopped at several auto part stores to check on the availability of sending units. Three of the stores were no help. At the fourth, the guy brought out a few units and we found one with the same same threads. It looked like it would do the trick, but it did not have the wiring pigtail on the end of it. There was a stud at the end where you would have to attach the wire. It was about $18. If I'd known for sure what the problem was, I would have gotten it.
I installed the oil pressure gauge. There was plenty of pressure. I decided to called the dealer to get his thoughts on whether the problem would likely be in the sending unit or my pressure gauge. He indicated they had replaced several sending units. Given I'd called him, I didn't have much choice and I ordered the sending unit ($38). Installed it yesterday and I'm back in business.
Bob