Bjorn
Do you want to race this boat in F18 class OD races?
The US Inter 18's were supplied with a carbon mast and larger then F18 Class legal main. The Inter 18 was also sold to Nacra Europe with an Alu Mast and F18 class legal sail and this boat was fully compliant with the F18 rule in Europe. (It competed at the time with Dart Hawk....) The design was replaced by Nacra with the F18 and later with the Infusion models. Some of the Inter18's in the USA were grandfathered into the NAF18 class with their carbon mast for a limited time. They were supposed to purchase a class legal mast to update the boat by some date certain.. You prospective boat could have one of these rigs so you should check.
So, If the boat in question has a carbon mast you won't be F18 class legal. This is not a problem though if you just want to go racing in any open class race in your area. If you are rec sailing... just keep the paint touched up and enjoy a nice ride.