I thought I would share as this might help someone else. For the past couple of months, my LR slides have had a pretty loud squeak right at the end of extension or the beginning of retraction. I have been using dry lubricant on the bars, gears, and pistons with only the slightest improvement.
Today I figured out what was squeaking. The steel plate circled in green on the left moves up and down when the slide is extended/retracted. It doesn't move much but just enough to produce a huge squeak as dry steel moves on steel. A spray of silicone on these plates (2 on each slide) eliminated the noise!
Ignore the overspray -- I was silicone happy just to solve this nagging problem!