Why would you swap the KSU? If you're willing to go to that much trouble, just default the KSU.

I know there are several points of view on working on older systems, but this is one of the reasons we no longer will work on an STS. The STS has been out of production for over a decade, it's time for the customer to move on.

Not trying to sound harsh here and I admire your desire to help your customer, but you've put a lot of work and research into making this STS work for the customer. Will you make enough money to cover all of your time?