I once had to fill up at one of those ghetto gas stations, they only had two choices, either regular or supreme, the supreme octane level was 98 which I was surprised with and wanted to try, so I got that. As I later found out, my car did not like that gas at all, it started doing the same thing it did when I put regular in it once, mainly the valves started tapping, performance fell and I only did 300km on the tank.
Went bakc to my old gas station, tapping was gone, mileage went back up, and all was well.
Morale of the story, don't believe signs on ghetto gas stations.
1985 190E 2.3L - a constant project.