Best stuff I ever used. Go to your local GM dealer and get a can or two of Rust Penetrant and Inhibitor, GM Part Number 1052627.
This is some of the BEST stuff I have ever used! When I had my Tercel in '03, (it was a '95) I sprayed all the nuts and bolts I though might have to be removed in the next 5 years or so with the stuff. It made rusty old bolts look BRAND NEW! I sprayed the Scion under the hood with it just now, and you can WATCH the rust disappear! I sprayed everything that I think might need to be replaced, the valve cover, horns, radiator hold-downs, etc. It will probably smell like burning oil for the new hundred miles or so, but the stuff REALLY WORKS!
Paid $9.03 per can (I thought it was going to be $12 a can) well worth it! Blows anything similar into the weeds, ie WD-40, PB Blaster, Liquid Wrench, ETC.