Can the slides be pulled out through the track windows or does the track have to come off?

no problem slidding them thru the windows. You might need a little w-d 40 to help but I have done all my sleds that way.

Check out this post:

Pointers (http://www.snowmobileworld.com/forum/index.php?showtopic=29498&hl=)

Skidudes right alittle WD-40 does its magic its shouldnt take u any longer that about an hour for both sides.

When should some one think about replacing the slides?

There is a wear line on them. When it gets close to the line replace. They will not wear evenly and usually wear at the front, right wear the SKid bends. It can be hard to see there because of the wheels blocking your view.