Gasket's are very cheap too, think even an official one is only a few quid so I wouldn't worry about it.
Rust, gearbox/diff noises and heavy smoke on start up or when revved would be more of a concern - a little dark grey to black smoke is no problem (ever seen a lorry going uphill?) blue smoke isn't great but a little especially when cold isn't worth worying about if you're happy with everything else imho, white is usually a bad sign but careful not to mistake steam for smoke. (oil burnt in engine is usually blue, oil in the exhaust especially a lot of it is white).
I bought a 1996 3door from worcester way, the guy advertised it as "a little grey smoke on startup" Went to fetch it, started it up and the smoke was nearer white and lots of it (oil as opposed to blown head gasket) He admitted it was worse than when he'd last seen it but it hadn't been started for a couple of weeks, seemed genuine enough so I handed over £750 and off I went.
The guy lived on a farm and his "drive" must have been about 1/4 mile long, Lets just say I wasn't impressed by the disco's red arrow impression - I stopped at the end of the drive and got out to find oil dripping out of the exhaust (shot turbo I suspect) it drove fine but I'd seen enough and demanded my money back - to soften the blow I let him keep the £50 and walked away, thank god he'd had the decency to give me my dosh back.
There's always gonna be tossers out there, just take your time and dont hand any money over until you're sure.
Last tip, if you're buying it for laneing or offroading ignore the paintwork - the shinier it is the worse you'll feel dragging it through bushes or mud (and it will happen).
