In most RVs the correct way is to NOT grease the slide, ever. Unless you have some specific instructions from GB to grease yours, I would not do it.
Grease on the gear mechanism just attracts dirt and is of no particular value on a rack & pinion gear that turns only once in awhile.
If you feel you must lubricate it, use a dry silicone spray.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC