Nice Post!
50 hours is right around the corner for me, although JD does not reflect to do so...
I wouldn't mix oils.
Oil mixes with oil fine, 80w will blend will 50w & 40w... they allstarted as "dino grade".... all are "miscible" as the chemists say..."mixable" in RWT...
Danger is in detergents and other "trade additives" companies put in their oils but may not specify type or even have to... different detergents could (not necessarily would) interact to lose some or all detergent properties... or worse case scenario "throw a clot" (?)
Unless you are low on oil and need to move ASAP, I would stay with whats used, which sucks for me, because Wal-Marts 45 min away, and closest dealer 1.5 hours! I keep extra...
P.S. If you check most 5 gal pails have "manufacturer codes" that specify which specs the contents meet/exceed. Better to have the extra $$$ for diesel, way I see it!
P.S.S. For veteran members... if you are changing hydraulic fluid before recommended, do you see particles in it if you drop a magnet into the bottom? What about gear oil? I know it "sits", but is that something the maintenance minded replace in excess of recommendations? Particles in it?