Take the Isolator out, cut the shaft part about 1/4" below the square block portion and throw away the the rest of the shaft part. Get a stainless steel 1/4-20 screw and insert it through the trolling motor bracket, through the isolator block, and through the deck. Install a stainless steel flat washer and then a stainless steel nyloc nut on the bottom. Tighten up and forget about those isolator washers every going bad again.
I've never liked those whole isolator inserts. The basic concept works well to keep noise and vibration down, but I've never liked how they hold down the motor. They always work loose over time, so I modify them for my own needs (just as an "isolator" and not as an "isolator/fastener" and install them with real fasteners. Never have a problem after that type of install.
All the best,
Glenn