It’s probably been 30 years since I’ve used marvel mystery oil but the can itself was amusing to read… some of those very old motorcycles ran ok and I always hoped it was a good thing. On the other hand, I had a friend who was a helicopter pilot at McGuire AFB who usually only rode his motorcycle from NJ to his home in Maryland every weekend, put over 100,000 miles on that v-twin air cooled engine. Thats a lot of miles for that engine…The mechanics there at the base helped rebuild the motor with him and mic’ed and measured everything… he told me then there was so little wear on parts that he did not replace things he swore would need to be replaced.
He used Marvel Mystery oil religiously despite Harley telling he would void any warranties in place doing so.