As a Broker of mostly smaller boats and Ribs, I would say the following: -
If you brought the boat to us and asked us to act as brokers, then without any supporting paperwork we would have to decline. The more paperwork you have the better the chance of selling and the better the price achieved.
Vat paid proof is going to be important to anyone wishing to export or use the boat abroad. The manufacturer of your boat may well be able to update you on the vat status and provide a copy of the original purchase invoice showing the vat (if paid).
An "MCA bill of sale" is useful but not vital if you have a purchase invoice and proof of vat payment.
We would also provide our clients with a legally binding contract covering such issues as outstanding finance, legal ownership, vat status, etc.
I'm not trying to sell the benefits of brokerage here, but you can probably see why some people think it's worth the 7.5% we normally charge to have all the paperwork properly "chased up" and legally executed?
I would try the manufacturer for the Vat issue and the previous owner if you don't have a purchase receipt. It shouldn't be impossible to get these things.