[john hall]

Can't honestly say I have torn an old Kohler down but seen dad do countless ones----I always seemed to help serve as "engine and cast iron grill hoist". Let me throw out a suggestion from a machinist standpoint, not as a mechanic, as our definition of flat generally is a LOT tighter than the rest of the worlds. You mentioned you flat sanded the oil pan. OK, lets assume its flat, what about the block? I read some heli-coils were installed, was this in the block? What I am suspicioning is blisters around the holes in the block. Can you try setting the block and oil pan together with no gasket or RTV, while clean and dry. Then take a thin feeler gauge, about .002" and see if you have any gaps? If you find some keep going up in size on the gauge to determine how bad it its and then figure what needs to be done--maybe just a honing stone will solve the problem.