There was a place at Rantoul that sold and serviced them called Shore Sales. I think Motomco went out of business but Shore continued to use their frame to develop a digital tester from what had previously been an analog machine before developing their own. It appears yours is a hybrid. A google search turns up this outfit-maybe they bought them? At any rate i bet they can help you. They will send you a loaner and you can use their packaging to send your meter in for repair-if it’s repairable-it’s not on their list. But I would wager they can. Ag Express might be an option if they cant. 

 https://moisturetesters.com/