Here you see the intercooler cleaning apparatus at work. That window is filled with cleaning solvent as it runs through the system.
I'll post a before/after picture of the intercooler tubes tomorrow.
In the event, once the cleaning solvent had been running through for a while, cracks started appearing in the covers. I suspect temperature differences played a role here.
With a change from dirty cleaning fluid to clean, the cracks opened up even more.
Eventually prudence dictated when to stop with the cleaning, as one of the cracks finally started to leak.
All in all, I guess I ran cleaning fluid through the intercooler for a good few hours.
That intercooler is as clean as it's going to get, short of taking if off completely and getting it professionally seen to with ultrasound cleaning.