I've owned hk's for several years now,(hk94.sl8.usc and 5 clones). I just found from a life long friend a NIB HK94A3 from an estate sale. What I would like to do is add a paddle mag release to it. Do I have to refinish the whole gun or can the paddle area be touched up? Who would be the best to do the work? Thanks for any help I can get.