Your 1937 should be model #4203
your 1938 could be model # 4253 or model # 4266.
The 1940’s should both be # 4266 with the small
cap being on the highest serial number motors as
as it was used at the end of production as you
have suspected. Always remember that a ton
of these were sold and parts did get moved around.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.