Jan Gougeon discovered the slop issue many years ago. He tried lots of fixes, with a monster resource at his disposal for technical fixes (the Gougeon company). He even tried the ultimate in mechanical fixes, a tapered hole with a matching taper pin press fit into place. All of the machanical fixes eventually came loose.
His fix - epoxy the head into place. This did not work for Ken, however he might not have created the necessary conditions for the epoxy to work properly. Epoxy does not bond well to steel, particularly steel that has had some oil or grease on the surface. I've been bonding my tiller heads for years, and have never had one come loose.
Here is my method for bonding...
1) Remove the steering post and clean it really well. Make a mark where the post sticks above the bushing.
2) Degrease the top of the tiller post and inside the tiller head.
3) Sand the top of the tiller post (the section above the busing) with coarse sandpaper, 36 grit works pretty well. I make a cross-hatch pattern, but straight up and down the shaft works good too, maybe even better. Sanding scratches going around the shaft don't do much good.
4) Sand the inside of the tiller head with coarse sandpaper. You want the sanding scratches aligned up and down. Again, scratches which are oriented 90 degrees to the shaft won't do much good.
5) Pack the tiller bushing with grease (this is your only chance).
6) Grease the tiller post and put it in the tiller bushing.
7) Degrease the top of the tiller post. Do a good job here to remove the grease, the bond depends on it. It won't hurt to give it one more sanding also.
Mix epoxy and collodial silica to a thick paste. Here is an application where collodial silica really pays off, it's the strongest of the epoxy fillers.
9) Smear epoxy indide the tiller head and on the tiller post.
10) Assemble the tiller head and push in the roll pin.
11) Wipe off any excess epoxy and let cure for at least 24 hours.
12) Go sailing.
The sanding and degreasing are critical steps. The degreasing is obvious, grease is an excellent release agent. The sanding is the real key. Epoxy does not bond well with steel, even under ideal conditiond. The Sarns parts have a smooth surface which does not allow the epoxy to get a mechanical grip on the surface. The coarse sanding scratches provide the mechanical "bite" which the epoxy needs to do it's thing.