Had this happen to my one and only paddle in the surf yesterday. I'd like to say it was maxed out and huge, or, you should see the other guy. But no it was only small and the board must have just hit it the wrong way.
So with the help of a drop saw...
I cleaned off the rough bits, cut a piece off the extension part ( I never used the full length anyway), shoved that in as a dowl.
And then some part A and part B.
Then Bob Naish is your uncle!
Now in contrary to the title of this, I only realised I could do this after I spent onefiddy on a new one and was about to throw this one away. It took me a full day to have "light Bulb" moment. How not so clever am I.

Oh well, at least I have a spare