The inventor of the GM OLM was on these boards fifteen or more years ago. Knowledgeable but he fought with Amsoil people got ticked off and left after a few weeks. I believe his thesis was that the OLM was set for conventional oil (at that time pre Dexos) and that oil quality (within limits obviously, no Crisco) made little if any difference, hence the Amsoil distributor battles.Rather than go through the hassle of fighting with them, as long as I paid for the conventional oil, I'd shorten the OCI. Then add it to the long list of reasons for why I do my own work, after kicking myself for taking it to the dealer.