I don't know much about R53 superchargers. But, I can't think of another way for coolant to get into the throttle body.
I have an R56, and the turbo is both oil and water cooled, so there is coolant running through the turbo. I don't think the supercharger on your R53 is water cooled, but I could be wrong. If not, the coolant would have to originate before the supercharger, and pass through the supercharger.
I wish I could be of more help, but I think you are on the right track with a leak ahead of the supercharger.
This is a odd problem. I would not drive the car at all till this is solved. You are just asking for more to happen if you do. The water pump PTO runs off the back of the SC but even if the back of the water pump had a bad seal it could not get in that way. I will have to go look at my car. I am trying to remember where the coolant meets the intake system. Its early I can't think.
That would stink. There have been no weird start up noises or chattering from the SC gearbox...just a general loss of power and bogging/unresponsive to quick/heavy throttle changes, but it was still drivable. I'm definitely not driving it now until I resolve the issue, as it went from being annoying to horrible. Thanks.
Maybe your caps exploded pressure and it's gotten into your intake. I know I didn't have a cover over my intake filter for a while before I got my new one and one time my radiator cap blew out and coolant collected in my intake box.
The throttle body is before the supercharger so coolant there would have to come before it. If you just have it in the bottom of the pipe before the super charger it may be from the seal inside. But that would only sit there when the car is not running. Do you see coolant in the intercooler? Oil gets in there but there should be any coolant.
See if you have coolant in the intake pipe before the throttle body and in the EGR tube. If it is in the EGR tube then you could have coolant in you oil and you're looking at head gasket among other possibilities.
opcorn:
