I have a 30-year-old Hercules MK2 and have been driving it for several years. I’ve been using a synthetic oil for all these years, but I’ve been having problems with it for a few days, so it doesn’t go on anymore or after a short time. Now a neighbor who knows something like that is probably all full of slag from my synthetic oil or something. He meant best to clean everything up and then to mix a mineral oil in the fuel instead of He’s right, or I can use the synthetic one.