87 is the first year of the 780, and the only year with a live rear axle, as opposed to IRS. This means you can get rid of the Nivomats if they go bad. IPD sells a conversion kit that includes springs and shocks.

87s can have deteriorated insulation on the engine wiring harness. Check carefully for this, as it is a real pain to replace.

A total of approximately 7000 780s were made from 87 to 91, so they are quite rare. Interestingly, that is very similar to the production total for the 1800ES.

The worst flaw is the scarcity of replacement parts. Most interior pieces and all the sheet metal, glass and exterior trim (well basically, everything but the powertrain, some of the suspension, and HVAC)are different from other 700s. Usual caveats apply - Nivomats are expensive, the B280F is not as snappy as a B230FT and is harder to keep alive, but as you pointed out the low mileage bodes well. Keep the oil changed regularly, ideally with synth to eliminate sludge buildup, and don't be afraid to push it (helps keep carbon buildup under control and certainly won't hurt anything that isn't already broken) and it'll be fine, it is a strong motor. I have one with about 180k miles, driven very hard for the last 50k, and no complaints except exhaust manifold leaks. If it's as nice as you describe, I'd have no hesitation buying it, but I would never again put myself through the hassle of trying to piece one together as I've been doing (no door panels, various other odds and ends missing... should have just cut my losses and scrapped it but way too far into it now). It is a real pleasure to drive, smooth and comfortable. Make sure the pusher fan ahead of the AC condenser spins freely, two of the handful of 780s I've seen in Nova Scotia were fire-damaged from melted wiring harnesses due to that fan seizing. I'd have expected that issue to be more widespread among the other 700s, I thought it was the same hardware, but I have only actually seen it happen on 780s. Coincidence or bad luck perhaps, but given the cost of 780 grilles and lights I take no chances. Pay attention to the rear side windows too, a foolish design oversight resulting in trapped water means that most 780s have severe rust inside the bottom frame of that window. Though entirely hidden by the outside trim, it rots the bottom edge off the window frame and eventually rots the body below the window. As it progresses you'll see the rubber trim above the chrome starting to bulge out. In a pinch I fabricated replacement frames for mine, but they may be available from the dealer or occasionally a good used set can be found. Make sure the door panels are secure, and that the power seats work properly, including the memory-glide function when the seat is tilted forward for back seat access. That aside, pretty much just the usual 740 stuff applies. Enjoy!
--
Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina