I've had my '86 S3 for 16 years - its been a fantastic car and I def recommend an S3 - Less to go wrong than in a Turbo, cheaper to run and all the looks.
Check all the usual things as you would a normal car. In addition check the exhaust manifold is not cracked, tyres can be tricky to get hold of - original Goodyears are no longer available. Try to speak to the specialist who has looked after it.
If its a good one you'll never regret buying it
Bazza