Sorry thought it was this boat http://www.ribraid.com/for-sale-2005-ferryman-8m-rib/
Owner may have seen it getting built, but I doubt he stayed for the whole build? If he has been using it off Islay for a number of years then no doubt, due to the prevailing crap weather- the boats hull and structure must be assumed to be sound!
You could always get him to take it across the pond to Redbay and get them to cast their eye over it.
If you know the owner, he knows the boat, it ticks your boxes but you are aware it may be a limited market when you choose to sell, and you get it cheap enough then what have you to loose? As I say, I know a few people with Ferrymans, outboard powered, but who have had no issues.