Combine was allowed to get dirty in the first place.  Apparently they are supposed to be kept under a blanket in the the shed and only driven when the wind is just right so dust never blows from the back or front. Supposed to wait till proper crosswind so all dust-chaff is blown away from the combine on the sides.  As is did get wet,, all the wiring is junk.  Your lucky it doesn't show signs of being actually stuck at some point in its history.

As is,, might get 1/2 a penny a pound for it, probably goodyear tires so $10.00 fee for disposing of those, plastic is worth about $1.25 ton. 

If you catch the junk man on a good day,, he might haul it away even if he does take a beating on the hauling charge being worth more than the green pile.

.

 lol !!! 

On the other hand give it a bath run it grease it, change oils,, and lt'll probably last forever though most don't believe it...

(Just powerwashing dropped the price $50,000 apparently..)