This is the part that will challenge me. Just so I understand correctly. Left side: there is a shim under the racer that helps adjust preload. Right side: the shim is on the side cover, looks like a metal gasket. This also adjust preload. I assume I will be assembling and reassembling the gearbox a few times to check and adjust preload. Once preload is fine I then will adjust the backlash? Once I do the first assembly will I know the exact shims I need or will it be trial and error?