Re: Opinion wanted on what to do.
Fiirst.. deep breath... spun couplers are common, the MOST common cause is from not lubricating the splines on the drive shaft BEFORE installing the outdrive... mis alignment can cuase it, but I'd put money on the dry shaft....
What you need to know is this, is the rubber spun or is the aluminum spun.... Aluminum= lubrication, rubber= alignment.
The grease on the shaft takes up the excess play between the shaft and the internal drive splines on the coupler, with out the grease, the splines work back and forth until they shear the aluminum... ooff center/alignment kind of explains it'self.
Heat risers full of rust are also common.... not that big of a deal, the rust flakes off from inside the riser and clogs the small holes,if the boat was not exibiting signs of over heating, remove the risers, clea out the rust in the small portsand reinstall...