This is the only pic I have on hand of the local stream:
The stream's water is absolutely the clearest I've ever seen, and you could see a the grain of a tiny peeble in water several feet deep. It is also the stream that causes the most gunk to collect on my line.....lots.

I'm always amazed at how many times I need to wipe the line to get it clean after fishing there, and I fish there quite a bit. It's possible that you had water wick into the core, but: 1) I don't know how long it takes to wick water along a line. 2) The nail knot should have compressed the line, and
might slow any wicking on a single trip. 3)People have used un-sealed tips for quite some time, and the tip still float.
Note: If I don't clean the line right after fishing (rare), it could take a few wipes before the gunk starts coming off.
P.S. The tip on the GPX line is on 6":
http://buy.scientificanglers.com/lin...-fly-line.html
It's still workable, but you don't want to cut to far into the front taper.
PPS: The "Dry Tip" of the SA lines is supposed to be due to microballons, and I don't know how much water they would absorb (if any at all). I've called
SA in the past, and you can get a tech on the line quickly. I actually spoke with the guy in charge of line production once. I had a spot on a new GPX line that
had very little coating, and he sent a new line to me that afternoon.