Agree with NazNomad, BUT - vinegar (especially the white, cleaning variety, rather than brown, malt vinegar) will most probably be fine on the nuts and bolts, but on "large" plated sheet metal parts that are visible when playing, you may well end up with flakes of plating coming off in your hand, leaving you worse off than before.
1st off, inspect the sheet metal parts closely and look carefully (bright light & magnifying glass?) for any areas, especially around sharp edges, where the corrosion has penetrated down to the parent metal.
2nd, if no "rusty edges" etc, seen, try vinegar on one part which is not too visible (if such a thing exists on your instrument).
If you do find corrosion deep enough to make vinegar a risk of removing the plating, try,
A) Careful, not too hard, MANUAL polishing with something like Solvol Autosol. That may well bring it back well enough that it doesn't notice too much from more than a foot or two away, OR;
B) If that doesn't work, find some 3M metalised self adhesive tape - available in "silk" or "glossy" finishes, ali, SS, and chrome finishes, and in several widths. Get a width to suit the widest part of plated metal you want to cover (IF poss), silk or gloss as you choose, but silk finish shows up less afterwards. Clean thoroughly with acetone, getting the surface as smooth as possible, NO loose flakes. Use a hair drier to warm the plated part, and an old smooth teaspoon as a burnisher, start at one end and carefully spread the tape along the length of the plated part, a bit at a time, warming and smoothing down with the spoon as you go. Overlap around the back edges and trim off with a knife. For the 1st try you may need to go at it a 2nd time, (!!!) but you'll soon learn NOT to kink the tape!
I did this on a bathroom tap which SWMBO particularly wanted to save and it's still there, looking good after about three years daily use. NOT easy, but do-able.
Good luck, let us know how you get on.
AES