Have been down this road with our 2188 and I don't envy your predicament. We broke the top sieve which we welded up and fishplated with 1 1_2" x 1_4" flat iron to get through harvest one year. In the winter the dealer changed the c channel supports to the 2388 style cast x and changed all of the bushings, which we and the dealer thought were the culprit. The next harvest, our reinforced top sieve split in the exact same spot as before. The shoe arms also cracked, with the left one actually breaking in two allowing the top sieve to flop against the bottom sieve and crack it too. Not fun. Ours appears to have been solved by shimming the play between the shaker drive shaft and the bearings. The play can be measured with a dial indicator set up above the big end of the shaker shoe drive arms and gently prying upward with a prybar. Ours was at .014" on the left arm and .013" on the right. A piece of .010" shim was wedged in between the shaft and the inner race of the bearing. If I had more time and different shim stock, I would have removed all of the play. Even as it is now, the combine is quieter when it is running empty as the slight knocking that the shaft made is gone. Shimming the left side takes about 15-30 mins, but the right one is more fun. Working behind both elevators adds a slight twist, as well the shoe drive pulley and slip clutch have to be removed. If you need more specific info, post here and I will email you.