I'm suggesting that once you separate the MB from the F6 you could potentially do the removal/replacement of the plastic wheel yourself. Now give that a wheel some serious lateral pressure to remove it and make sure you're turning in the proper direction. Unless your thumb-tip is white you're not leaning on it enough! You can't possibly do any further damage. Carefully place a wide rubberband between your thumb and the wheel for better grip. I'd guess the splines were stripped when you intended to unscrew it but were inadvertently tightening it.