If it is a rack & pinion gear driven slide, it doesn't need lubing. If hydraulic, maybe a dab of lube on the pivot joints once a year.
What you see and probably think of as "seals" are actually just wipers on the sides and top/bottom. If you feel you must, spray them with a dry silicone or slideout seal lube once or twice a year. May keep them a bit more supple.
The actual seals ae D-shaped rubber tubes on the slide flange, inside and out. They press against the sidewalls when open or closed. Again, a dry silicone or fancy "RV slideout seal" spray 1-2 times a year may have some long term benefit. (I don't believe it myself, but it won't hurt.)
The typical problem with slide seals is that they can detach from the slide and sag or fall completely off. That's an issue with the adhesives or staples used to install them, or a result of something getting trapped between wall and seal. Cast an eye over the slides when both in and out and be on the lookout for a wiper (flapper) or seal that is starting to get out of position. That's when you want to get proactive - fix it before it gets worse and tears a whole section loose.
OK, now all you people who religiously lube and condition their slide seals every trip or every month can start throwing your spears at me...