Oh buddy.... sooooo many things could be wrong. First this should be posted in the repair forum but it is ok I'm sure.
Low compression is usually going to be a top-end issue unless your seals are not seated properly on the crank shaft sides. The leak is going to be at the base or the head of the cyl.
I would address the top end leak possibilities before breaking down the whole bottom end a third time.
I am also assuming you have a proper "gasket" on your case halves.