I’ve run older cars on 10% ethanol gasoline without ruining the fuel system. When they first started adding ethanol to the gasoline, I had to change out all the fuel filters, since it dissolved the gunk in the fuel system. I heard stories about some owners having to change out fuel filters twice.
That was my experience. Your mileage may vary.
Changed the fuel filter already. RPMs dip when I first start (it’s a manual) and each time I change gears, then it revs right up. Can’t figure out what is causing the dip in RPMs.