I just checked on a place that I used a couple times 20+ years ago, but he's no longer there.
With built in gps, sonar, and networking with other electronics, electric trolling motors aren't what they used to be, so repair may be more like electronics repair these days.
You may want to check out the trolling motor sub-forum of bassboatcenral.
http://www.bbcboards.net/forumdisplay.php?f=128
And I know Minn Kota has service centers in MA. You can use their service locator to find them.
Report back on how you make out.