Hi,
This is as far as this breather hose seems to want to go into the supercharger.

It looks like it should go in until the ridge meets the red part. On the other hand the part of the breather line that's going in is discolored compared to the part that's showing. Trying to figure out how much force to use on this 20 year old plastic.

 

EDITED: It does appear to go to the ring in the first video below (Mod MINI). See below removal footage; full screen and frame-by-frame it at about the 2:45 point. Supposed to 'gently' push down on the red ring (a pair of bent / angled head needle nose pliers comes in handy) while inserting the pipe until it seats. That said, there appears to be a margin between the line and the red ring in the second video at 24:30. You are correct after 20 years (or 10 in harsh climates) the plastic becomes brittle. Watch out especially when hooking up the black plastic intake pipe to the supercharger at the green ring, the bypass valve hose, and the two additional vacuum lines (one for TMAP, one for the brake booster) for the same reason; they all love to crack, providing instant, nearly impossible to find vacuum leaks. Silicon spray and taking your time are your best friends on this job.
Also this one, removal at 6:47 shows pipe seated to the ring, then the ring well above the seat after replacement at 24:30:

 

I managed to pull out the red part altogether, but it still only goes down so far before it stops

 

I stand corrected; maybe.

From the first video it looks sunk to the line. Also in the second when he first removes it at 6:47. But in the second there is a distinct margin (though the red clip is in place) when he replaces it. You can see this starting at 24:30. Also confirmed this on my own car just now; was able to peer between the upper radiator hose and the intercooler to have a peak with a flash light. I did the same job a year ago but could not remember whether or not this was an issue at the time. Like you I must have just pushed it (gently) in until it stopped and released the red ring; definitely did not want to force it. I have had no issues with it since.

 

Is a piece of trash or part of an old tube in there perhaps. It does seat all the way to the ring as seen above.

 

Wow, you didn't have to pull your engine just to show us that.

 

Sorry if this is way off base but are you sure it's routed correctly?

 

That’s a fair enough question. I had the same thought which is why I went and pulled the engine out just to take the above pic for them

(the later is for comedic effect. I’m not that crazy, or am I?)