The 5 Relates to horse power and 39 is the year.
I have one of the 9.5hp. models. It was the look that
got me interested in getting one. Starting it and its
performance convinced me I didn’t want any more.
I’ve been told that the smaller hp. motors (5 or 6 hp.)
not as troublesome.
https://www.youtube.com/watch?v=-_rZ4zjYgn4
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.