I had the same problem on my 08 Classic a couple of years ago.(Oil on back of engine like the rear gasket had gone).I thought it was the head gasket but on close inspection the oil on the rear of the engine didn't come up that far. Took my bike to stealers where they told me yes ,engine out new gasket on rear of engine. WRONG! It was the oil seal on the rear diff unit that had gone,sounds crazy but true . Not sayin it's the same on yours just lettin ya know.Triumph came good and replaced under warranty.