I just got a nice green 2003 discovery with 54,000 miles on it. Awesome vehicle, the only thing I did was change the oil, it wasn't changed for 8 months, only driven about 1500 miles in those 8 months, since it is June and warm I went with a mobil 1 1040. 1st question, any good manuals to suggest?

 

the link in my signature will take you to the RAVE manual and all the electrical diagrams.
i recommend checking your front drive shaft to see if it has greasable ujoints. if it doesn't, i suggest replacing them with greasable ones. it is a known failure point on D2's and can result in the destruction of you transmission/transfer box.
other than that, welcome to the club!
jon

 

And you might want to check out our tech section, and get started on the 60k miles service list, review the rebuild method for the mentioned prop shaft, and the oil questions write up. You would also want to look at an Ultra Gauge to read and reset cdes, plus have digital display of coolant temp, factory gauge does not show you the whole story. UltraGauge Automotive Information Center and OBDII Scan Tool $70. Flush cooling system of all things "dexcool" and go back with green colored 50:50 coolant. Dexcool makes sludge. As it fills up radiator you run hotter and hotter, but like slow roasting over hickory coals, it takes time. Radiators are pools of chemical reactions, and those actions go on 24/7, just a little faster when heated up. So age, not just miles, dictates cooling system sludge. Overheating and front popshaft are two major issues. Search forum for info on the replacement thermostat, soft spring, will run truck 6-10 degrees cooler. Spin both your electric and viscous fan to be sure they can work. And consider an external oil PSI gauge or at least an oil PSI test from time to time.

And have a great time!