Are the fronts of your drawers hitting the cabinet face? Are they hard to operate? They're probably tilted down, because the rear support has collapsed. Here's how I fixed it.

There's a support framework to hold up the back of the drawer slides. It rests on a piece of thin lauan. That in turn is supported on the sides by a 1x1" chunk of pine, which is only held by staples through the lauan panel on either side. The weight of the drawers can pull the staples through, leaving the back of the drawers basically unsupported. The result is the back sags, the front of the drawers is no longer square to the cabinet face, the drawers are hard to operate, and they make contact with the cabinet face.

This is an "after" picture, with the drawer slides square. More pictures at the link above.

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Good to know. Thanks for your post.  Drawers in my 166 have not sagged (yet?) as you described, but they would not stay closed while underway.  I installed magnetic latches on all of them.  That solved the problem.
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HAHAHAHA  I just re read your title....you said SAGGY DRAWERS...
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