As the happy owner of a Petrol SIII I would recommend going petrol if you are looking at a series or an early 90 but otherwise go diesel. Benefits of petrol is that they're slightly easier to fix at the side of a road, e.g. a spark plug goes you can fix it pretty easily but if a diesel injector goes its a garage jobby normally. And because older vehicles are more likely to break down hence, go petrol. Diesel pros are that you can enter water, provided you don't go below the engine air intake, without fiddling under the bonnet before smearing Vaseline and wd40 all over the electrics. Also you get a lower torque band which is better for serious off roading although in my experience its only when you're properly stuck do you need it and admittedly diesel mpg is a better than petrol. Petrols are a little faster off the line too but with a Landie speed isn't exactly essential. Hope this doesn't cause too many objections and is helpful