Some time ago the engine light came on and the odometer said “gascap”. I checked it out and it was OK but the light and “gascap” stayed on. I took it to my trusted mechanic and after some diagnostics, he turned to a Chrysler bulletin manual and discovered that it could not be fixed and the only way to remove “gascap” was to reset the odometer every time you start the car. Meanwhile, do I drive with the engine light on all the time? Pretty scarey!
I would get a second and a third opinion for this problem. I don’t see resetting the odometer as a fix for your vehicle. I would not “trust” your mechanic at all with this kind of advice.