The cylinder lock for Park is both electrical and mechanical. In the rear of the lock cylinder, there is a cable which can get sticky over the years. Use some graphite or locksmith oil to make sure the cable can move freely. You will have to remove the plastic clamshell over the steering column.

Spraying oil/silicon on the shifter button can help. So can spraying the override button, but don't use much oil. Oil attends to attract dust/dirt and dries after a while making a big mess.
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