I have never heard of the valve seat explanation.
But, if the gap is too wide on your spark plugs, the engine would miss. Recheck the gap.
I'd also make sure one of your spark plug wires hasn't shorted out, as well as checking out for a good connection between the wires and the boots.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".