Power Steering Rack and Pinion Replacement

My garage says there is a leak in the system and that the system needs to be replaced, which is very expensive. I notice no steering problem when driving, the power steering fluid remains full and I have no leaks on my garage floor. Another garage recommended this before, but they also made a number of other recommendations on items that did not need to be replaced. How do I know if the leak is serious enough to replace the whole system? Should I use a power steering leak fluid to see it is repairs the leak?