Had an interesting conversation with someone that contacted me today. The front of his Rio gold was cracking by the welded loop (i actually cannot stand welded loops on trout lines but that's another story). This was a brand new line.
My first thought was "it's got to be the leader". It was basically down to not having a heavy butt section/taper, so the line was hinging. A common thing in the UK is to fish a level section of tippet all the way through, around 8Lb on still waters, so i would imagine it's like casting the fly line without a leader at all.
I used to fish with braided loops many years ago with the plastic sleeve, however this always cracked by the sleeve within a few months, and i think it was down to the non flexible sleeve creating a focus point on the line when it unrolls (would you agree?) Even with a tapered leader!
If i have to use a braided loop, i whip it on now and use some Aquasure to seal the thread. It's very flexible and the cracking problem goes away.
However for my trout stuff i just needle knot the leader onto the fly line.
On a different note, who remembers cast connectors?
All the best
Nick
Do you use a needle knot Lasse on the MED? 
if needed to glue, a flexible glue would be my choice. Pulling the core into itself and under and then out through the coating, and then welding the coating around the tag end is my prefered method, no whipping and no glue. 
