I had the oil changed in my 2005 F350 6.0L diesel a month ago. I had it done at Sears because I was travelling and the local Ford dealer couldn't do it for 4 days. I now have an oil leak coming from the drain plug. The bottom of the oil pan is stained from about 1 inch in front of the plug to the rear of the pan and up about 4 to 6 inches. It is also stained clear to the left and right sides of the bottom of the pan. There are no oil stains on the upper portion of the pan. To me this means that the leak is coming from the plug and not above in the main engine area. I'm still travelling so I don't have any tools with me. (Yes, I could go buy some.) I tried tightening it by hand, but no success. I haven't personally changed oil in my vehicles for over 10 years now (3 vehicles ago), and I recognize that lots of things have changed since then.
By the way... I've only ever had the oil changed at a dealer since I bought the truck, 47,000 miles ago. I wanted to use the dealer but I couldn't wait, so I was stuck using Sears, Wal-Mart, etc. No way was I going to trust this vehicle to Jiffy Lube, etc.
So... I have a question, before I go back to a local Sears automotive... Does the drain plug have any kind of gasket or washer on it?