I thought this game was manufactured by Sega itself? Years ago I remember there being threads that listed games with a high failure rate and I don't remember The Little Mermaid being mentioned, I can't find them again to check. If there is a list you've found I would appreciate a link so I could read up on it. I remember the Tengen games being mentioned a lot like Grind Stormer, for whatever reason they were manufactured differently than other games.
Technically replacing a Tengen board with a standard Sega board isn't really correct as it's not original, but it's generally acceptable as the replacement is reliable and still 1st party. A modern aftermarket board would actually work as a repair but I personally avoid games with aftermarket parts like that, same with replacement labels. Using parts like that might devalue your games, so it's worth keeping in mind if you're repairing anything valuable later on. I just wanted to clarify that it could be repaired with an aftermarket board if you really wanted to.