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Was this a dealership that is telling you this or an independent shop?
The rack and pinion on your Mustang is electronic, no more power steering fluid or power steering pump. There is a TSB out for lower control arm bushings where we replace the lower front control arms and install shields for the bushings. Below is the TSB.
I highly doubt the rack and pinion is bad. Even if they replace it, they will need to program it to the vehicle for it is a module within itself. The system is called PSCM (Power Steering Control Module). As for the inner tie rod ends, they are replaceable separate from the rack and pinion. I would have them perform the TSB first and reevaluate the front end noise.