Century IV Flight Directors

One of my major areas of experience is autopilots. One of my customers has three small King Airs
with Century IV flight directors. Maintaining these systems has been challenging, to put it mildly. I was hoping to hear from someone with hands on practical knowledge of these systems.
I did autopilots 20-25 years ago and got a Commercial pilots license and an A&P in support of the whole autopilot effort.
Between then and now there was fifteen years of component level Weather Radar bench work in South Africa. Now i find that autopilots from my time are getting pretty old (just like me).
Mostly, the older systems should be replaced with something new. My customerf find that the price of a new system is high (got that right). I, personally, don't like the way an STEC flies and don't like the company's attitude when it comes to trying to support their systems or their customers. Bendix-King long ago lost the thread of what customer support is about, so that's out.
So, we are left trying to keep things flying that are getting pretty tired.