what are the problem areas of the 98 buick ultra with over 100,000 miles?
timing chain, rubber parts degrading, O2 sensor needs changing, sparkplugs / ignition wires change.. your owner's manual has the service requirements.
motor mounts, tie rod ends,
Front struts, rear shocks, and the rear shock mounts. Those rear mounts are a particularly bad design. They only last about 40,000 miles. I've also had a fuel pump quit running ($600) but that was at 145,000 miles. Overall, I had a '97 and now have an '04 Park Avenue ... best two cars I have ever owned.
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