Contrary to popular belief, the supressor was not fitted to protect the SCU.
It was found that electical noise, generated mainly by motors, was causing the SCU to trigger other circuits.
The solution was to fit a supressor to reduce the electrical noise.
Other than the common issue of water ingress, the SCU suffers from failure of its control relays and also failure of the circuits that drive the relays, this results in things not working (windows) or being on constantly (horn).
These faults are relatively easy to fix, the only snag is that the relay used in the SCU was a component that Pektron had custom manufactured but this can be worked around if you know what you are doing.
There is an issue where the SCU cannot have new fobs coded to it if it is in the armed state and the original fobs have been lost, in this instance I believe that XPart will suggest that the only solution is a new SCU and fobs.
Avon Diagnostics have developed a tool that allows an "armed" SCU to be unlocked without original fobs and thus new fobs can be coded in the normal way.