The between-the-lens shutter can be serviced by any competent camera repairman. As Jon says, the focal plane shutter is simple, and can usually be serviced by anyone with moderate mechanical skills and a few basic tools. For detailed information try to locate the Army manual TM 11-2352. These occasionally appear on ebay and online booksellers. Prices vary: patience saves money. My 1950 version covers Pacemaker and Anniversary models. One time-saving tip: mark the position of the shutter curtain before disassembly so you reassemble it without trial and error. The Pacemaker series uses a governor for some of the focal plane shutter speeds. This governor can give problems with those speeds.