As others have said, get a price on how much he rack and pinion would cost to replace and then use this as a part of the deal.
I once bought a Corvair that both the dealer and I thought needed a valve job. I bought the car at a very low price figuring that I could live with the problem until I had vacation time, then taking the heads off the engine, sending them to a machine shop and then putting the car back together. We hadn't had the car very long when we drove it when we went out to eat. A sudden rainstorm came up and the car ran so poorly I didn't think we would get back home. I replaced the distributor cap and spark plug wires and the car ran beautifully. I had a real buy.
Even earlier, I bought a television set that had a problem with the sound cutting in and out. I got a good price and decided to take a chance. The seller told me that the set had been in the shop several times, but the problem was never solved. I pulled the chassis out and found a cold solder joint at the volume control. A minute with the soldering iron and I had a great television set that we used for years.
Sometimes, buying something with a problem can be a great purchase.