We found what I think is the best way to apply the seal treatment when the RV has slide awnings. In fact, my DW did this two weeks ago as I worked on installing the rear tank heaters!
First, use something safe, like a 3 step step-stool. HD and Lowe's have a variety of heights and steps usually in stock. Extend the slide until it is about a 8" to 12" (20cm to 30cm) from being totally open. At that point, it is easy to reach over the top of the slide while standing on the stool. Soak a paper towel - we used the "box of paper rags" you can get from HD, pull the slide seal inside while wiping the outside of the seal. Go back the opposite direction to wipe off the excess. The using the soaked towel, push the seal back out while wiping the inside. Again, return and wipe the excess. She had to adjust the slide extension a couple of times to complete the job. But she did a really great job in no time at all!
The outside seal on the exterior slide wall (the EPDM white seal that sits against the RV) was more difficult. Basically soaked a paper towel and pushed it across using a long dowel. Definitely more "hit and miss".
You definitely do NOT want to use grease on the Lippert rails! The rails have a "gear teeth" on their lower edge that ride in the cog to extend and retract. The attachment shows what these "toothed bars" look like retracted inside the RV underbelly. The toothed rail rides inside of a U-shaped rail, open at the bottom, by a roller at the far end and the cog at the outside edge. If you put grease on this gear, it will make a mess inside the underbelly! The hydralic piston mechanism is usually at one end of the slide next to one of these toothed gear rails. (The exception here is the bedroom slide where the hydralic piston is centered between the toothed gear rail.) The rails are "joined" by a gear and "axle" so they are driven out by the piston equally at the same time.
Now, if you have used grease on the toothed gear rail and plan to clean it, might I suggest using something to plug the hole in the I-Beam from which the rail extends. Basically, the U-shaped rail is open at the bottom to the inside of the underbelly. That is, if you direct a power-washer or hose at where the toothed gear rail enters the I-Beam, you will fill up the underbelly of the RV with whatever you are spraying! If you have used grease, you might want to remove about 3 or 4 of the self-tapping screws holding the coroplast and reach up with a paper towel "wetted slightly with solvent" to clean the grease from the inside.
I used Dry Silicon spray this past weekend along the full length of the U-shaped rail and on the toothed rail.
While I'm on the subject, it might not be a bad idea to remove 3 or 4 of the self-tapping screws holding the coroplast next to the hydralic piston mechanism. Gently pull the coroplast open (down), and peek inside using a flashlight. (Love my Surefire LED flashlight! Small with a powerful beam!) There will most likely be a small puddle or two of water built up from condensation - warm air entering the underbelly, cooling, and dropping the now excess water out. This usually amounts to a cup or two of water. But look under the hydralic piston mechanism to see if there is a "red puddle"!
If there is, you might want to tie a paper towel on a stick with a couple of rubber bands, extend it inside the underbelly area and "sample" the puddle liquid. If it is red fluid, you probably have a hydralic system leak or fitting not properly tightened. Use a clean paper towel on the stick and wipe one fitting, turn the stick over, and wipe the other fitting. If the fitting is leaking, this will allow you to assess which one it is. Otherwise, it might be the hydralic cylinder or the hydralic hoses leaking.
Ron