Hi James Welcome to GTOUK You are in the Right Place lots of Knowledge and info here. First check these http://www.gto.club/resources/buyers-guide/
Here are some of the more frequently asked Q & A's
Convince me - #7 by adam.leslie1991
Couple of important things , Rust on side sills and rear end , timing belt kit when it was replaced , regular servicing documents , not heavy mods , also check DVLA MOT history. Before buying take someone who knows these cars with You to see and hear it if possible.
Lots to come 
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