The farm here uses....  http://www.schaefferoil.com/  and they swear by it... Most of they're 3406 Caterpillars, E-7 Macks run 50000 miles between changes. All the farm tractors get changed once a year. They always pull sample and send to  http://www.blackstone-labs.com/  They haven't had an engine, trans, differential down since they switched over 15 years ago. They have pulled the pan and rolled in new bearings at 500,000 miles on one of the 3406's but there was no copper showing on the old bearings. Probably some of the best lubricants on the market today.....!!

contact person, Alan Bradley....  abradley@dmv.com

I don't use enough oil myself to have the Schaeffer man pay me a visit, so I stick to Mobil 1 synthetic products.