If I needed to make a permanent repair on that, I would probably do something containing elements from all the suggestions so far:
- clean the split as much as possible (if necessary, kerf it as per Kendall). If other laminations are starting to go, kerf them as well.
- get as much epoxy as possible into all the split(s) then clamp til set
- Now, using a router table, or very carefully on a table saw, remove about 1/8" of material from all 4 sides of the last 6" or so of the epoxied end. Round the edges of this new area as well
- Wrap this area tightly with glass cloth and epoxy. Build it back up to the original thickness.
-re-drill the boltholes
Finish with a good UV-stable coating, like a two-part urethane, or good spar varnish.
I defy this to split again.
(on the other hand, maybe a new tiller is justified

)