The aluminum tanks crack, from vibration, on one of the motors I have an interest in. I use Red Coat in them to seal the leaks and hopefully help in holding the tank together. I can have one of them on the boat for a month or longer running 2 to 3 times a day weather permitting. I have never had any issues. I get the tanks clean, and the use some type of cleaner with a mild acid, diluted with water by 50%, to etch the tank for 20 to 30 minuets, or until it stops foaming. As you describe your tank it may not survive the etching. That’s a pretty common motor. You should be able to find a better tank and possibly less than the cost to seal your tank. Check eBay. There are all kinds of them on there from serviceable to near mint condition. Tubs
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.