If you know what wrong with it you can buy the parts online. I just bought a complete lower motor assembly on ebay new from a authorized minnkota dealer cheap. I ordered it Monday it will be here today. There not hard to fix. Google Minn Kota trolling motor assembly, there is a link with a complete DIY on line.
My brother had a nagging problem w/ his Minn Kota 3 years ago and he had it fixed @ Greenwood Lake Marina. He was very happy w/ the service and they were quick & reasonable.
I just checked on-line and they are not listed as factory authorized service any more. You might want to call and ask.