Tron - right flipper sticks

Recently purchased a Tron pro. I've noticed that after a few games the right flipper begins to stick up during game play. It goes down after the game ends or if you engage the opposite (left) flipper. I'm just wondering what I should be checking before I just randomly buy parts. Thanks.

I'm going to take it apart tonight and order parts ASAP. Thanks for the help so far.

So I finally had some time yesterday to pull the coil out and look at the coil stops. The coil sleeve was grimy. So I cleaned the sleeve and fired the game back up. I've played multiple games on it and it seems to have done the trick as the flipper doesn't stick anymore.
The new issue I now face is the right flipper makes a loud humming sound when its engaged. The left side doesn't do it, only the right side. This wasn't an issue before I cleaned out the sleeve, so I'm puzzled. I was planning on buying a rebuild kit but now I'm curious what could have caused the loud sound.

Any input is greatly appreciated.

I've checked the EOS in test mode and thats working just fine. any ideas?