Where the heck are you buying M 1 oil that's $13 a qt? It's 7 bucks / qt round here all day. You didn't say anything about the MC specific oil so I'm assuming you're talking about regular M 1 automobile oil.
As for the diesel skeptics, don't look at it from an RPM basis. Yes they turn very low RPM compaired to our bikes but, if that was the case they would use something like honey or syrup. The oil pump still has to provide flow and volume. so it would probably have a hard time moving something so thick.
If you want peace of mind about diesel oil, think of it this way: most diesel engines you run accross in automobiles are turbocharged, which creates more pressure in the cylinder and produces a greater potential for "blow-by". Diesels also operate on much higher compression than your standard gas engine. Along with longer oil change intervals, diesel oils have to be formulated to withstand the extra stress, compression and blow-by (that will dilute oil to nothing short of colored water) that comes from operating in such a harsh envireonment.
Oh, and for those that were wondering, 15w-40 ( the "w" is for "winter" not "weight" ) is your standard diesel oil, our bikes require 10w-40, Shell doesn't make that in synthetic but, they do make a 5w-40 which will cover our bikes' need and since the majority of us want to run synthetic, this is what we use.