+1 on chassis rust. It is repairable but relatively expensive unless you are a VERY competent welder.
Good ones are out there, I bought mine 2 weeks ago and it has very little rust in between the rear axle and the rear bumper so I've flatted it down and given it a good Waxoyl-ing.
There's not usually a big rust problem on the body of a DII but you need to give a good look all the same. Above the windscreen is a favoured spot.
When I'm looking at DII's I want to see if the vehicle has been enthusiastically maintained or not, so the first place I look is the air filter box, the oil filters and the fuel filters. It's not a matter of cost with these items, more an indicator of the previous owners view of maintenance.
I'm just coming towards the end of my initial purchase rectification, here's what I've done and costs:
1. Engine oil change and both oil filters (oil and filters came in the deal) - cost Paddocks filter kit £20
2. New air filter - in the above kit;
3. New fuel filter - ditto;
4. New serpentine belt - Paddocks £11;
5. Renewed brake fluid - 2x400ml £8
6. Renewed coolant bleed screw - new ally one, about £4;
7. Gearbox, transfer box and both diffs oil change - 5ltrs of MTF94 £33; 6ltrs of Spirax £13.5
8. New fob case for 2nd key - Ebay £2.75;
9. Grey waterproof seat covers -Ebay £18.75;
10. New brake pads all round - Paddocks/Mintex £30;
11. New front passenger window regulator - Paddocks £25;
12. 2nd hand PAS pump - Ebay £30.
13 WaxOyled the chassis - Ebay £25 for 5ltrs of black.
So total spend approx £210 plus my time. Taking into account that I bought my lovely sept 2000 ES manual Disco TD5 for £1400, I reckon that's a pretty reasonable spend.
She's now running like a bird in flight - just beautiful.
Hope that helps?
Dave