A few things I would definitely check out before buying would be, the engine running performance, turbo performance for operation and check for leaking seals. The rear self leveling system would be a biggy on my list, as most of the parts are high dollar to replace and may be a bargaining chip in your favor. Interior cosmetics of course must be to your liking as well. I'd check naturally for rust, mainly in the rear under the wrap around rubber end bumper pieces. Does this one have a third seat or just a storage tray? I'd also check out the normal things like A/C, blower motor fan (have history of squeeling, bad bearings) headliner problems etc. Everything else is pretty much the same as any other Benz for that year and chassis.
Sounds like a fair deal if everything is in place and working as it should.