Jackson_Slugger
$50 Site Donor 2022
Looks like another alternative to turing regular oil into a HM one. No idea about pricing or availability:
GT-1® HIGH MILEAGE BOOSTER - Kendall Motor Oil
Kendall® High Mileage Booster is a unique concentrated blend of key additives, specifically tailored for higher mileage gasoline powered vehicles. GT-1 High Mileage Booster increases resistance to corrosion and helps to improve engine cleanliness. GT-1 High Mileage Booster, when used as directed...
kendallmotoroil.com