You would be correct on that one. Also when you want to lap a flat surface you need a flat surface to start with. Another note about lapping is you want to work the pc in a figure 8 motion to give equal pressure in all directions.

Razor ol man... the first thing thru my cranial labrynth was what Tom said. I would guess that the locating boss is a tad undersize and you got the same kind of little blowby burn spot on top of your sleeve.
I seem to remember it being a compression beast.