What parts should be replaced when the shift lever locks in park.

quite often its just needing cleaned and lubed, some have been sluggish from coffee or cola spills, pull some pieces and inspect the workings ,maybe just adjustment of the locking tab

The dealer did loosen the wire around the shifter and it worked for a week and then froze in park.. Any other suggestions?

that wire feeds 12 volt to the disconnect solenoid, if broken , no disconnect! look in operator manual most have a override method to release if battery has no 12 volt to energize solenoid

And you do know that stepping on the brake is what sends the power out to do this and if you have no brake lights you have no solenoid release ! a simple fuse?