Lately I have been noticing a significant decrease in gas mileage, without changing my driving habits. Are there any common issues in a high mileage M20 that could potentially cause such changes? I have gone from ~15.5avg to 12.9 in a matter of a few weeks.

I know there are many, many things that can affect gas mileage, but if anybody has thoughts, PLEASE share them. I'll be selling to car soon, and eventually replacing it with another E34. (Don't worry, I still love 'em.)

Help!