Every time the ignition timing is set the car runs likes new! Within 500-1000 miles the timing changes on its own (for the worse). Symptoms manifest themselves as rough/low idle, mis/backfiring, reduced power on acceleration, pinging. Symptoms come and go until the car becomes nearly undriveable. Within the past year I've changed the fuel regulator, fuel filter, convertor, coil, wires, cap, rotor. Mechanic suspects the distributor is worn. Anyone rebuild one, or know of a place that specializes in rebuilds?