Now I am not a fan of Weathershield either, but if your going to come on the site and bash a product you should take the time to explain the issues your having a little better. You do not mention where the air infiltration problem is, you do not mention why the potential service issue is Weathershield and not possibly a distributor service issue(which is not necessarily Weathershield) Is it possible it is an installation issue? How old are these products? Have you don any maintenance on them? Has the distributor or company you purchased them from inspected the units? Are they would or vinyl units as wood units require different care then vinyl would? So, please explain a little further before issuing a wide ranging blanket statement.

As Millworkman said, it's possiblly an installation issue....especially if it is a newer door.

Is the unit plumb, level and square? Most times I find the air leakage is caused by the side jambs being bowed in, or the stationary panel not seated all the way into the jamb. Or it could be the operating panel rollers are not adjusted properly. All installation issues.....

We spent ten's of thousands of dollars on Weathershield sliding doors. The biggest mistake I ever made. For those of you who think it could be an installation problem, let me just say this: I have been in construction for over 35 years and I think I know how to install a door unit.
We have multiple sliding units which are drafty. As bad as that is we also have two telescoping units 16' x 10' that leak water. The threshold doesn't drain well and what does drain leaks into the house. We have removed the units and re-sealed the openings but with no success. The unit leaks where the threshold meets the jamb. Contacted the local dealer again 3 weeks ago about the ongoing problem but nothing from Weathershield. I thought we had done our homework before we bought, but it just goes to show anybody can get screwed.

Weathershield = Piece of S---!