You can't actually search on VIN number on the Forum, Colin. Theoretically 3-letter terms are searchable, but in practice it doesn't work. Adding the "#", as in #442 to make it 4 characters, doesn't help either! So, without a User-name, you're lost. Maybe Tim has the VIN and member real name/User-name relationships, from the original full-member Forum registration, but that is not public information anyway, I guess.
Sometimes members publish their real names in posts, say in their "signature" for example, such as "Colin Murrell", so searching on a known surname may just help identify a possible user-name. Long shot!
David