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.