Opened up my MP5K because of problems it was having at the last game. The selector switch itself was going between positions like is should and felt like it was new out of box. But....it would only select safe and full auto and full auto would cut out and had to be within a few mm area to work.
Took down the gun all the way to the gearbox, (I'm to scared to open up a gear box still) V3 gear box. The black selector plate has copper tabs on it that touch copper tabs on the mech box when the selector plate is moved. I noticed that they were bent down and dirty. So after a good cleaning and some minor bending back the gun seems to be in great shape. I just need to take it out for a day to see if it gives me anymore problems. WOOT!