My 1996 Disco appears to be burning a slight drop off oil. I suppose with 145000 on the clock this is to be expected. What I am wondering is what would be the heaviest grade of oil that I could put in or can anyone recommend a good oil to use. We are not at the disappearing in blue smoke stage but I notice a small cloud starting to form every so often

Stick to recommended spec oil for your engine, trying to go for a 'thicker' grade will more than likely cause more problems than it will solve, as oils don't behave as most people think they do.