It is my understanding that the original mag releases in the 908 were plastic and that wear could result in the situation that you are describing. I believe that the entire release assembly would have to be replaced since you can't even reassemble them once they are taken apart - the magazine release button/nut is a one-shot press-on deal.
Give S&W a call and see what they say. I understand that the newer mag releases are metal and won't have the same problem.
The early orginal mag catches were plastic and did wear quickly, now they are medal, easy fix if you want to replace it yourself. Order a magazine catch, magazine catch nut and magazine catch spring. To remove the old one insert a proper sized punch through the nut (the button you push to release the mag) and tap out the old catch. Note which way the spring is installed and reassemble in reverse order. The nut is still plastic and is a friction fit to the catch so anytime you replace the catch or spring it is recommended you use a new nut.