I'm currently using a Blend of Shell Rotella, Triple Protection, conventional 10w30 and Formula Shell 5w30 conventional all in SM.
The Shell Rotella, Triple Protection, conventional 10w30 is, IMO, hard to find but the Rotella 15w40 in Dino is everywhere here in the NE,along with the Shell Rotella T6 5w40 Full Synthetic and T5, Synthetic blend, 10w30.
It's the Shell Rotella Triple Protection, 10w30 in Dino that is hard to find....IMO....because of the low price and retailers would rather stock the higher priced T5 Synthetic Blend. Who knows how much synthetic is in the blend?