This is a low hour coupler that been sitting in the boat for about 10 years,

garbage? or would you use it?

Need to see the splines. Can you get a head-on shot looking at the splines? They should have flat tops, not pointed tops, if they are in good usable shape.

the splines are in perfect like new shape, questioning the rust on hub were it meets the rubber

thats a HP coupler...........is that green paint under the black

yes it is a HP coupler , pay no attention to the green spot, I dropped something on it,lol

Its all risk reward. Are you willing to pull the engine to replace it if it fails.
It may be perfectly fine for many more years or the rubber may have deteriorated and it may not last an hour.
I guess I would question, why all the painted over rust?? It could actually be 25 years old. No way to know for sure.

Yup, what Griff said. I had both of my motors out and while one coupler was bad (splines were shot), the other was good. I still replaced it because I really didn't want to pull a motor again for a $600 part. Yeah, sucks to spend money if you don't have to, but who the hell wants to pull a motor again after just pulling 2?

I agree, thanks