ORIGINAL: gaRCfield
Ken, I'll have to check this out. I don't remember seeing how tight the seal was after I cranked down the screw, but what you said makes sense. The only thing I can think of is if the plastic tubes are soft enough that they are deforming rather than a good tight seal being made.
If this is the case then I would recommend replacing the plastic tube with brass or aluminum tubes before using any sealants.
Ken