When the car stops, try to determine any information about the three components required for an to engine run. 1=fuel, 2=spark, 3=air. when you have all three in the right proportions and at the right time, an engine runs and takes you to the store. You can eliminate most of the spark problem with an MG when you put the $100 petronics electornics ignition in.
Mechanics today correctly have to "shotgun approach" a problem because of the complecity of the current cars and the high hourly rate the shops have to charge to stay in business
We have the advantage because our cars are prettty close to basic. I would suggest that your approach could be to get informed about your vehicle and how it functions. Then find the sports car nuts or classic car nuts and go visit them. Every one that I have met were very good people.
Until you as the closest to the problem can get enought information when the problem occurs no mechanic that I know can tell you where to look.
Get informed and the classic car nuts will rally around and give you all the support you need.
Jim Lundgren
gztracker