I know someone that has an older vehicle with about 170k on it that runs perfectly. Plugs are dry when pulled and inspected and the engine (GM) has plenty of power so it makes no sense to do a reman engine really at this point. But, the rear main has recently started to leak a little. They change the oil every 5k and have to add a quart every 3k or so. They have been running Amsoil (since about 75k) like I do on mine and the thought has come up that maybe the Amsoil is so clean that it contributed to the seepage. So, I think they are going to try some Bar's Leak or something similar to see if that helps the rear main to stop leaking. So, what's the general consensus on continuing to use Amsoil in this situation? Think it would be better to keep using it, or switch to a conventional oil? Just curious what the local oil experts here on the board recommend.