Some earlier ones emitted a clicking sound from the rear of the bike and Honda did a recall. Some may have slipped through the net and it is worth listening out. The differential bearings can sound rough and Honda used to recommend that the diff was not serviceable and to buy a new unit. 1987 1200's were a lot quieter than previous versions. Some wheels have been known to strip the drive splines, all for the want of a little grease.
Plastics are generally quite robust.
The trunk lid usually cracks at the corners and around the hinge mount. The panels are quite expensive and so are the stripe kits, so a cosmetically good and well looked after Goldwing with a high mileage can often work out a better buy than a low mileage one with tatty panels.