Sounds like your'e looking at one for ptretty much the same reasons as i did recently. I needed a tow car and previously (15yr ago) had series landies but discounted them because of the low mpg, i love range-rovers but the older ones i like are pretty rusty now. Then came along the disco mk1, this forum steered me towards a 300tdi and i must admit its a lovely motor. I paid £1800 for a 1994 ES with 120k on it, leather seats and WORKING aircon
It looked sound and had a "new" mot on it, that turned out to be a lemon for various reasons. Since buying it i have fitted a new cambelt, both fanbelts, rear hub oil seal, rear brake pads, clutch slave cylinder, new track rod and joints, steering damper, exhaust downpipe, 2nd hand turbo and a full service.
Luckily i'm handy with the spanners and hammer and i'm mid-way through a new boot floor at the moment.
The list might seem like its a crap car but i dont think so, the chassis is totally sound, and the bodywok apart from the boot floor seems fine too, the engine burns no oil and is returning 30+mpg on mixed route. Now i think that for a 16yr old car is a pretty impressive mpg figure considering the 2300kg weight of it. It will also tow the hell out of my trailer with an 1800kg load on it, you can hardly tell its there.
So, if you are not afraid of doing your own service work and want a fun and comfortable motor, i would get a 300tdi, but do check for chassis rust and have a quick peek at the boot floor, expect rust if its not been fixed, how much will vary, the cost of replacing my one will be about £150.
Do a cambelt change for peace of mind, and check the coolant header tank for oil etc as a sign of head gasket failure.
Dave