This has been a reoccuring problem w/ masterbuilt units since day one. I had one of the first MES40" in baton Rouge and after 9 months had to do a repair.
The best repair we on Smoking meat forums have come up with is when you have to open the unit up to do a repair go ahead and replace all the wiring and connectors that you can access. Go to appliance repair shop and buy stainless connectors and 12 Gauge high temp wire. The unit comes w/ aluminum / tin connectors and 14 Gauge wire. After the repair my 1st MES lasted 6 years before the cabinet rusted out. I now have the newest model and have not had to repair it yet.
www.smokingmeatforums.com and do a search for MES repairs . will show you everything you need to know.