I am fairly certain that the occasional enrichment is due to the plunger "sticking" in the fuel distributor, despite it being cleaned by the technician. The car is still very hard to start when hot, so I am going to order a new fuel pressure regulator tomorrow. As fuel pressure applies a counterforce to the plunger against the air flow force on the sensor plate, I am hoping that this new part will also resolve the plunger "sticking " issue. The fuel pressure regulator on the car at present appears to be original. If the new part does not resolve the sticking fuel plunger than I will buy a second hand fuel distributor. Does anyone know if the fuel distributor from a 380, 500, or 560 will fit my 420, or if the plunger can be somehow machined to stop it from sticking?