Paul
Get it surveyed before you buy it, if there are faults they will help in negotiations.
A surveyor will also give you an opinion on the value of the boat, the cost of any repairs and guidance if you ask him to.
What the ultrasound sound survey says is, that in 2006 the hull had a certain thickness, the amount of corrosion is dependant on how thick the steel was in the first place and how well it has been maintained.
If the boat was 'blacked' then (2006) it is now due, approximately every two years is the advice.
The BSC only says that in 2007 (test date) the boat complied with the testing requirements, it does not mean it is now compliant.
As to contacting the original owner, give it a go, the worse that can happen is he tells you to go away.
Sorry no advice on moorings.