My Mercedes Benz SLK350 (2006) had error codes 0301 and 0351 (rom Auto Zone

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The above codes came on when it was misfiring (which i explained to them is random).I took it to the shop, and they found other codes (I'm sure...it is a 2006). After looking at their codes, they found the bumble flap to be loose. They repaired these..and i was hoping it fixed my problem. They felt it would possible fix the problem. They did switch the coil to another circuit without a misfire or new code..which is no surprise since the misfire is random. Am I being unreasonable in my frustration that I paid out 1,400 to have the tumble flap replaced, (because it was loose) and still having to take it back, and now paying for a stupid coil replacement?! (He showed them the misfire codes, and explained this was when the engine was running)