Been using it in all mine for so many years I can't remember how long! Been using it since late 70's, early 80's or so.
Only exception is the hand start A that sometimes gets used in the winter. Though I don't often use it when it's this cold (the cab is nice and roomy but a bit drafty & chilly) that 15-40 is mighty stiff at 0° and lower! Makes a feller groan a bit to roll him over! In that cold weather he gets blue jug Wal-Mart 10-30 until spring!