The closest Pep Boys to my house - that I know about - is in Everett, WA and they carry Mobil 1 Formula M ESP 5w-40.
NAPA in Seattle never has Mobile 1 ESP 5w-40 on the shelves.
Seattle area NAPA auto parts stores usually have a compliant Valvoline Synpower fluid on the shelves.
The Valvoline part number is vv966 (that's vee-vee nine six six). The NAPA retail computers can look this up by vv966, if I recall correctly.
It's Valvoline Synpower 5w-40 (or was it 30?) MST, though MST isn't always on the bottle.... this product is or was on the MB 229.51 spec sheet.
All the spec sheets are at bevo.mercedes-benz.com
See this thread for more talk about the Valvoline alternative:
https://sprinter-source.com/forums/showthread.php?t=6789
-Jon