I bought an '81 Citation new and had Ziebart undercoating put on it. All that did was delay the inevitable; by the time I unloaded it in '87 even the hood had rust holes. Went from bad to worse as I then bought a used '85 Pontiac 6000 STE, the worst POS I ever owned. In two years I replaced the steering rack twice, fuel pump, oil pump, coil, ignition module, rear calipers. I never did fix the power antenna or power locks. Even the radio blew out. Had the A/C recharged several times. I'd like to think they have improved the quality but my BIL's 2003 Impala isn't much better.
GM chased away a lot of customers with the junk they built in those days.