Reinstall the cover???
(Just kidding!!

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You could try something like NeverDull, but it probably wont work, and sometimes NeverDull
WILL dull plastic (the bobbins).
I would go directly to the little wire wheel used in a Dremel tool. That would work really well for something like this, but you've gotta be super careful not to scratch up the bobbins, IF you're concerned with them looking nice.
Use masking tape to protect the bobbins, and if you can even use it double thickness to be sure the bobbins are well protected. 2 strips of tape running the length of the bobbin, with the tape edge just touching the poles to give max protection to the bobbins. Then use small cut up pieces between the poles to protect the area of the bobbins between the poles.
If you tape the pickups pretty well, and use care when using the Dremel, that rust should definitely come off, and your pickups will still look kewl!!
(BTW, if you dont wanna knock yourself out with cutting up all the masking tape, and you happen to have a paper hole puncher, you could always just cut squares of masking tape (I would still go double thickness), punch a hole in it, and do the poles with the Dremel individually.

)
(There is a worst case scenario here too... if the poles are ultra-rusty and you cant get the rust off any other way, you can always sand the entire top of the bobbin (light paper, like 320-400 grit) until the rust comes off the poles, and then use a combination of finer and finer grit automotive sandpaper (like 600-1500 grit), and then liquid plastic polish (the stuff used to polish motorcycle helmet faceshields) to get the bobbins shiny again, but thats a lot of work, and again, you gotta be careful, especially with the plastic polish. You dont want any liquid getting in the pickup windings.)
