I had 4600 jacks on a camper built in 2004. This Summer several of the jacks started out really stiff and making noise. Three seemed to recover but one failed entirely. I called Tweetys and they sent me a 4800 jack. I was very happy with the service. Jack was shipped that day from Georgia and arrived at my house on Long Island in under 48 hours. The 4800 jack is a few inches longer. I understand that is necessary because some truck beds are more elevated than in years past.
The Tweetys rep told me I should have run the jacks up and down about twice a year. I don't think I used them more than 4 or 5 times in the 8 years I owned the camper. I certainly never tried to take them apart and do any maintenance.