I just recently went through the same thing, it was coming from the lower connector near the fuel pump. The part was $20 at the local dealer, and yes it is plastic. Check with you nearest triumph dealer, they told me on certain bikes there was a recal on this issue, (my 03 955i wasn't part of the recal, but yours may be.).. Its reaslly easy to fix, don't over tighten it, and be prepair to see alot of gas when you disconnect it. If you have any problems finding the part you need, or a dealer near you, feel free to let me know and i'll find a way to get it to you from my dealer here on Long Island.
jiffy1867@aol.com