Stainless washers
I think the short answer is that there is no "official" part to do the job. On my Oday 23, the tiller is bolted to an h-shaped piece of stainless steel. This piece in turn is bolted to the top of the rudder. It's not clear if you have a problem with the connection between the stainless piece and the rudder or the stainless piece and the tiller. If you have play between the tiller and the stainless holder, leather works and won't mar the finish on the tiller, but it will disintigrate eventually. To fix the play I had between the stainless stock and the rudder head, I used a few stainless washers. If the problem is that the hole in the rudder has enlarged because of the play, you will have to fill the hole with epoxy and redrill it. Be sure to overfill it on both sides so that it really "sets" your repair in place.