We have the same problem with our 2 frts.
Our leveling jacks are HWH 13" straight acting 12k lb units, pt#AP9552. We changed the springs which helped, but not completely.
We applied all types lubricants many times without success.
We called HWH and they explained that they could overhaul the jacks for worst case $225/ea plus $30 shipping each way.
We removed the frts and took them to a local hydraulic shop in hopes of saving some $$$. They couldn't fix them mainly because HWH wouldn't supply them with info or parts.
So we called HWH back and made arrangements to have them overhauled. We shipped them a week ago and we should have them back in 2 or 3 more weeks.