First, you may want to move this to the GoG section. You will get a lot more people who are familiar with the Extcy looking at the post.
You have mentioned the front banjo (on top of the HPR) and a barb. Which is the leak coming from? The banjo is a female fitting in relation to the line and the barb is a male fitting in relation with the line. I bring that up because GoG suggested this was due to the line expanding in the heat. If the line expands it will only hold tight in the banjo and even on the barb with the nature of tube (with and I.D. and O.D.) I would think the expansion would still hold tighter.
Basically I am saying bull**** on GoG's explanation.
a) Is the leak from the banjo or the barb. With that info we may be able to help better.
b) (and more importantly) This is a new gun, therefore it is under warranty. A problem that you cannot fix should be rectified by GoG. Either by refurbishing or sending you a new one.