To me, GP's are like light bulbs, to be replaced individually when they fail. I lost my first GP and didn't know it, thought I needed a valve adjust. When I lost the second GP the car would only start after a long run up on the starter, the first one was still burned out. I ordered 5 new ones, changed the burned out ones and 3 are still on the shelf for a rainy day. The ones I had to change were no treat, #1 was tough, #5 was a b*tch. #2, 3 and 4 seem like they are no problem and may leave them to see if they cause problems or not. Checking them is a simple test to ground from the start relay plug.

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Doug
'83 300SD "Old Gold" 170,000 mi.
'82 380SL "Green Machine" 190,000 mi.

Some days you're the pigeon, some days you're the statue... I'd rather be the pigeon!