Oil leaks - if there are any, where do they come from? A sump gasket is fairly easy to fix, a rear crankshaft bearing seal is a bit of nightmare. Likewise, look for telltale green stains and trails from coolant hoses, etc. Ditto for brake lines and wheel cylinders. Look for damp carpets or ones with a rusty back. Talking of water, make sure that all of the diff and gearbox breather hoses and pipes are connected and in good condition. Also, take a good long hard look at the front end, oily leaks from the swivel hubs spell trouble and pay special attention to all of the rods - any bent one send a message that the vehicle may have been driven hard, especially if there is a lot of stone damage to the underside of the vehicle.