I would require 2 for base maintenance. One for outstation with availabilty of more for instances of AOG failures. This large old aircraft WILL require contstant MX but it's often quad redundancy allows for easy MEL procedures to keep her moving. I remember all the air driven devices having poor reliability given the number of them and age of the components more than a decade ago. Slat drive, acm's, reverser motors (P&W) etc are a constant. Not to mention I have never seen more tires thermal during hot and or heavy operation (pilots could have prevented much of this by allowing for a longer rollout).