Brother of The Benz, David
An article in the MBCA Star Magazine made note of combustion chamber pressure when the engine is driven with hard starts, full throttle exceleration.
The author made note of how the valves are slamed closed from the high combustion pressure resulting from full throttle application.
The price we pay for stoplight racing is short valve and valve guide life.
I know this doesn't help you resolve your problem, but the Star information opened my eyes and I'm looking forward to 200,000 miles before the cylinderhead has to be serviced.
Happy Trails Beep Beep from The Spiderman in Houston!!!