I had one jack that was really slow when I purchased my motorhome 2 years ago, I replaced the springs with the new style first and it did help some, the jack was till very slow. Eventually after the jack started leaking and wouldn't stay up, it kept lowering and causing the back corner of the motorhome to drop.
I contacted HWH and was going to send the jack into have it rebuilt. I was under a little bit of a time crunch so I elected to purchase a rebuilt one they had in stock for just a little more then the cost of the rebuild. it was about $350 shipped and took me about 30 minutes to move the sensor to the new jack and install it. pretty simple really.
good luck with figuring out your issue and getting it taken car of.
1998 Winnebago Chieftain WKL36L Diesel Pusher.
5.9 24V Cummins, 6 Speed Allison
Toad: 2014 Grand Cherokee, Limited, diesel