As I recall (from some v hazy days of yore on the RW fleets) a Comp Wash was "water sans salt" - ideally demin. If the cab failed PPI checks the cab got another "WSS" wash followed by another PPI. If that failed too maybe a 3rd WSS - but after that it was "Turco nuts". That was sort of last resort really before an engine change! Had moved on by the time this new-fangled ZOK-27 or whatever that was arrived .. Zork 27? "Mork and Mindy" anyone???? Cheers, H 'n' H