I bought a used pair of manual 4100's & 4500's and none of them have end caps; seller said they were motorized at one time. They are in good condition, with very light rust, and operate smoothly up/down without a load.
What is the purpose of the end cap kit which includes the cap, spring, plastic coupler, & washer @ $24 each.
I can buy (4) 2" square tube caps for $10 to keep rain and dust out when loading/unloading since my 70's fiberglass popup camper is to narrow to keep the jacks on full time. I will spend the extra $90 if the extra pieces provide some protection to the jacks or measure of safety during the loading/unloading operation.