I have a 1988 420sel that runs ecellent when it runs. First noticed problem that engine would die when I made a right turn. Would instantly restart and down the road I would go. Now, I can be driving in my neighborhood, and the engine will stall. Roll to a stop, try to restart, and it takes a couple tries for the engine to start. Sits there and runs, go driving and it will stall again. Let it sit and run in driveway and it will run for a while and then just stall. New fuel filter today, new fuel inlet line, new sparkplugs as Mercedes reccomends, and it still stalls. When running, runs without missing, smoking, just quiet and smooth. My guess now is fuel pump relay. Am I going in the right direction? Buy new or are used ok. This from what I can read is an issue when they get older. Help. Steve