Ctfarmer, are you the first owner? Has this ever happened before?
If the 3 point doesn't lower then it is turned all the way in and if it lowers and a high rate then it's all the way out.
If it is lowering then only turn the knob in a tightening direction and grasp that knob tight and crank it in. Sounds like it has been adjusted out rather firmly. It should not matter if the engine is running or not while turning the adjustment knob.
Another thought is Kubota's do have a tendency for the 3 point to bleed down, most noticeable with a box scraper attached. This can be compensated for by snugging up the adjuster knob to reduce and or stop the fluid from by passing. If you are not the original owner then maybe the seals are really bad and the knob has been substantially cranked in. As I noted, if you have an implement for weight attached and it basically free falls when lowering then the knob is all the way out.