Rear caliper repaired, now power steering is intermittent?

No the rear caliper has nothing to do with the power steering but there is a product that you can use that will fix the intermittent problem you are having with your power steering its called Lucas Power Steering Fluid and Stop Leak it is not only a stop leak but also Conditions the seals in the rack and pinion and will stop that intermittent problem.

Do not put this in your power steering resavoir!! for one VW and Audi uses Hydrolic mineral fluids so these lucus products will not work it will only break your seals and blow your rack and pump. Please discribe your steering issues in a little more detail. It can be possible that when they lifted your car off the ground the mount came loose or shifted or a tie rod moved. A couple things i would ask is Is it harder to steer left or right ? or is it periodic from either side? is there any play in the wheel where the wheels does not move while turning the wheels?

You know what they say about opinions everyone has one but I would not be recommending the stop leak if I have not tried it myself and it worked. Would be the first to say it did not work if it did not work. Now it is not a 100% guarantee that it will work but it will not make the leak worse if it does not work but it is worth a try.