There is no cam seal at the back end of the head.
If you are trying to narrow down an oil leak, get some UV dye and a light, add the dye to the oil, clean the area off thoroughly, then run the engine while watching with the light.
The only replaceable items that could leak oil in that area are the valve cover gasket (often requiring the valve cover itself, as I already mentioned), the tandem pump gasket, or the tandem pump itself. That's pretty much it. I doubt the cylinder head gasket would ever leak oil right there, I do not even think there are any oil passages at that end of the head. The end cam cap is a machined fit against the head itself, and is unlikely to leak any volume of oil unless it was off at some point and not put back on correctly.