Hello, while I’ve been at university my Mazdaspeed3 has been at home and used by my dad somewhat regularly since the lease on his car ended and he hasn’t bought a new one yet. Long story short, I recently found out he’s been filling it with 85 instead of 91 like I told him to do. He says he’s gone through about five tanks of 85 and I’m worried this may have caused unnecessary wear to the engine, or damage. I’m only in my hometown for today so I feel it’s unlikely I’ll get to see my car. Do I need to worry and do I need to do anything like siphoning the tank and using fuel cleaner?