2010 Mazda Speed 3 - Check Engine light -Cylinder misfire

I've taken my car to the Mazda dealership 7 times now to get a check engine light looked at. Each time my car is fine for about 2-3 months then the same issue happens again. Every time they say that a cylinder is misfiring when they run the diagnostic. They have replaced the replaced the cylinder, spark plugs, and fuel injectors, etc... but it keeps happening. They don't seem to know how to fix it so I was hoping someone here has seen a similar issue and has some suggestions.

Car: 2010 Mazda Speed 2 with 70,500 miles. I bought it new and have only taken it to this same dealership to get worked on. I love the car but this is getting ridiculous.

 

What is the code what are the symptoms. What had been done to the car?

 

Injector seals probably going to crap. Coil packs can cause it too. Try swapping em around.

 

I had to bring my Speed 3 in again (8th time for same issue) to the dealership because of the check engine light - this time I got the error code. P0302 Misfire on cylinder 2. They replaced a spark plug for the 3rd time. The car is still acting sluggish when I give it gas to get up to speed on the highway. They have done the following Replaced spark plugs, replaced fuel injectors and did "something" to Coil, ignition - they did not say in the Repair Order. I have a meeting with one of the mechanics tomorrow to discuss the issue. Any help would be appreciated.