[Keith True]

I think you are going to find it is combustion by-product.It will be a little sticky,and maybe have a little brownish tint to it.May smell a little like creosote too.It wicks out through the gasket filler material.There is no oil exposure that high up on the left side of the engine.You can get the same stuff oozing out from around the head studs sometimes.A truly flat head,deck,and torque does prevent it.