What not try EOS (engine oil supplement)...GM #1052367? Don't know if its still available but it is on eBay (http://www.ebay.com/itm/GM-Super-Engine-Oil-Supplement-Vintage-Can-NOS-Factory-Full-1051396-/382230382767?hash=item58feb4c8af:g:1uwAAOSwrlRZv~mi). As I recall, this product used to...