For the last 4 or so years I have had an oil leak draining down the passenger side rear of the motor on my 94 K2500HD 6.5L Diesel. It leaks down the side of the bell housing on the starter then to the ground. I am trying to figure out potential sources of the leak. I can see some oil residue in the valley toward the rear of the engine as well. At first I was thinking it could be the OPS, but I have read that it located on the driver side, so I am thinking that is not the issue. I am almost positive it is not the valve cover either as I had my transmission and bell housing off about 4 months ago and I had a pretty good view of the back side of the valve cover. It appeared to be coming from somewhere up in the valley of the motor at the rear. Can anyone point me at some common items that may be the source of this oil leak.