Ok for the record here is the update.
The toilet is Thetford Tecma Silence Plus.
The flush stopped working but then worked again late night until mid day only to quit just past noon. This happened for 5 days.
Sometimes the button just indicated a full tank when it was empty. This can be reset by turning off the coach power (sales switch) and back on. But it wont flush.
When I finaly found a new control unit and was able to install it (thanks for helping Dean Johnson), the part came with instructions that didn't show wiring changes that had been made by Thetford. Several hours of checking into this later it was installed and back to normal.
If you have original manuals for your coach showing this toilet and model and serial numbers be aware that Monaco removed the tags on install and ours has no model, serial and part numbers so save that manual.