I have a buddy from Paducah who blew his 2018 TG tranny. He had his 1,000 miles service done at Space Coast Harley while down in Florida and they put gear oil in his tranny instead of Sny-3.
The Paducah dealer replaced the whole tranny instead of rebuilding it. He wanted them to save a sample of the gear oil so he could at least get a refund for his 1,000 miles service when he went back to Florida. They said they "forgot" to pull a sample and save it for him. One dealer taking care of another I am guessing.
Another reason I try to do all my own fluid changes.
If they charged him the $$ for Syn 3 then I can see his gripe. Otherwise I would prefer a gear specific lubricant in the tranny vs motor oil which is what Syn 3 is.