I got a 200Tdi recently and it's bloody lovely. Unstoppable, but moody, but appreciative, if that makes sense. High maintenance, but a little bit of TLC goes a long way, and if you don't mind getting a lungfull of your clutch it'll go like the clappers.
You can get at most of the rust without pulling apart anything but the carpet in the back.
Frame is obvious. Check the tops of rails, outriggers, and have a feel behind the rear bumper. There is the odd ****ter out there.
Sills, lower pillars, and rear arches.
Engine bay inner arches, towers, batt and light boxes. If it's not misting it'll be rusty, so don't be put off by oil unless it's a proper leak.
Rear floor and step, rear arch inside door, bottom and hinge side of doors.
What you can't get to as easily is rear arch inside and footwells, but the sills and boot floor go first, so you've got a good clue there. If those have been done, expect to do the footwells next.
Unfortunately I can't tell you much about drivetrain since I don't know what it's supposed to sound like yet (bought it with a knackered pin bearing and it machined itself a new orifice), but do go over it, and don't be shy, unless it's cheap enough to sort out when you get it home (eg. I got a VGC front axle for 50 quid on ebay, 350 for a new set of goodyears). Engine off in neutral you can get underneath and wiggle props without a jack to hear play in diffs and axles. Wheels up for swivels, and it's perfectly normal to ask to have a couple of the wheels off when buying LRs.
When you start it up, give it a good stab to wake the turbo up before setting off, and check that you can find the gears and they work (diff lock and low range too, don't be afraid to ask where they are, can be a bit loosey-goosey). In cold weather just wait for the heater light to go out before cranking it. Don't bother with glow plugs, if it needs them it's got issues.
Brakes are brakes. It's a heavy vehicle. Be aware.
And if you're planning on taking it anywhere wet (islands off the west coast of Europe can be like this), buy your gear oil in bulk from the outset, and don't forget your wader plugs. Engine oil is cheaper in bulk too, and chances are it'll want a flush. ATF for the gearbox, which shouldn't need changing often unless it's got problems.
Hope that's helpful, and I do want to add : Please get one. Apart from the body rotting out and maybe being a bit of a tinkerer's dream, these are absolutely stonking motors, incredibly capable, and it's a terrible shame to see them getting scrapped.
