My 560 SL has been well maintained by MB dealers. It has 110k miles on it and last week it started to "misfire" and it seems to be getting worse. It happened originally when first started and idling and now it does it when you step on the gas.

Any ideas on what to check out short of taking it back to the dealer? It has about a 1/4 tank left so the gas was not added recently (not sure if that rules out "bad" gas).

Appreciate any input.