I'd blame the shims for the cutting out, not enough compression...as for the potential air leak, maybe you solved it with the screw. As for the oil leak, if it's at the back, then I'd say manifold seal, but have you checked the front bearing, that's a common source of oil...I can't say I'd fault your logic on most of those, and nothing else immediately springs to mind as potential causes...test it again and let us know what it's doing...