PAO's are one part of each oil's base.
Delvac 1 uses TMP and PE polyol esters.
M1 SS uses TME esters.
Delvac 1 has a higher percentage of AW additives such as Boron, and ZDDP. Delvac also has a better Detergent-Dispersant package for HD use.
M1 has higher FM additives, but a good set of AW adds (Moly, ZDDP, Boron) but at a lower level.
Actually, I would think they would complement each other.
I see no problems with mixing the two.
PS. If the M1 SS is 10W30 and the Delvac 1 is 5W40, expect a slightly different viscosity, such as an 8W35.
[ June 05, 2003, 11:07 PM: Message edited by: MolaKule ]