There's a plastic screw on the back of the focuser (not the 4 in front) that determines how tight or loose it can be..
Tighter, you get less slop in the barrel but harder to focus up and down. Looser, it's easier to focus up and down, but you get slop in the barrel.
Try that one.
If it's still bad, you can do what John Bambury does occassionally with his R&P (same as yours), and that's pull it apart and re-grease it with better lubricant. Apparently that can make a reasonable difference.
The other option, is to spend $100 and get a crayford from Andrews. It will bolt straight into your existing focuser holes in the OTA, and it is a 300% improvement on the R&P. Anthony (frogman) has the crayford on his 12" dob - did you get the chance to try it up at Kulnura?
The last option, is to spend $300 and get a
moonlite CR2. It's the top of the range, obviously. You'll need to drill 4 new holes into your OTA to mount it though.