On Thursday, November 27, 2014 10:41:33 AM UTC-5, Ed Pawlowski wrote:
In our Family Room we have a Pella 8' slider about 17+ years old. The
stationary side is in perfect condition, but the moving half has some
rot in the bottom panel. Not sure how bad it is, but where the wheels
fits it cannot be adjusted and that end is dragging. The aluminum
front panel is coming off, but since it is cold I don't want to go
tearing into it just yet.

Couple of questions and observations.
Aluminum cladding looks nice but can hide problems
A good door should have a much longer life
Should I even consider Pella again?
We have a Marvin distributor in the next town. How good is Marvin?
This is on the north side so it never gets direct sun. Aside from
insulated glass, does any of the low E stuff do better?

Other thoughts?

Most often rot is caused by water failing to drain away.
I'd take a good look at it and see if it's salvagable. If it's not
seriously compromised, removing the rot, followed by treating with
anti-freeze, then wood hardner and/or filler can often make it good
for a long time again. If it requires structural strength because of
the rollers, etc, then an epoxy filler is appropriate.