Keep the Discovery3 and get the jobs that need doing repaired. You could by a late Discovery 3, A Discovery 4 or a later model but you won’t know what lies in store for you. If you have a good engine and everything except your known issues are in good condition the Discovery 3 will last you many more years. I’ve actually seen now three Discovery 3s with over 300000 miles on the clock. The owner of one of the Discoverys was picking his truck up from Land Rover after having his third Cambelt fitted with 312000 miles on the clock. This was a 2005 Discovery3 and the engine was still as good as when he first brought it in 2007.