http://www.kodiakbs.com/service-and-repair-center

This site lists a number of service centers. I have a 505 in a 1985 DG 400, and as far as I can tell, it is identical to the much more common 503 in many ways, with some notable exceptions, like the crankshaft. My sense is that an outfit qualified to service a 503 may well be able to service the 505..