'07 cobalt, bad control arm rear bushings.
The bolt was badly stuck. After much struggle, I got it out. (Save time - be ruthless.) I can get a replacement bolt (11589009 M14X2X131, Class 10.9), from a dealer. But, the old nut is now useless, and there doesn't seem to be a dealer replacement for it. Class 10.9 is SAE Grade 8. All I can find locally OTS are Grade 5's. This URL , talking about frame bolts generally, says to use a "Grade-Gt lock nut". They sell a "nylon insert class 10 locknut" , which may or may not be what they were referring to.
So, my question is, for anyone who had to replace the nut, what did you use?
 Frame Bolts - Hex Flange Screws in Grades 5, 8, 9 | AFT Fasteners
 Zinc Locknuts Supplier - Wholesale Lock Nuts in Bulk | AFT Fasteners