I've got my MDC 1600 sitting right here next to me. My gauges haven't worked for a couple seasons. I opened mine up and it was dry as a bone with no corrosion. The dessicant package is still in one piece as well.
This past weekend we were on the water so I followed the troubleshooting link http://www.epicmarine.com/docs/MDCtrouble.PDF
and was getting 12 volts to both the red and purple wires on the 18-pin harness, so apparently it's my MDC.
I've been trying to contact Medallion via the contact info (phone/email) listed on their website. No humans ever pick up the phone and so far no reply. How long did it take you to get a response and what number/email did you use to contact them, if you don't mind me asking.