The racheting noise is caused as a result of the overrunning nature of the PTO engagement CAMs. The early design of the CAMs included an overrunning clutch as part of the PTO engagement CAM.
The PTO CAM was updated in newer models and does not include an overrunning clutch anymore - so no racheting noise.
The additional oil level PSB that you have applied (I do not) simply immerses the PTO CAMs in the transmission oil to quieten down the noise.
On TBN one (or two) users have reported a PTO failure. In one users case, he had multiple PTO failures. His tractor was primarily used for tilling. There was speculation on the board based on photographs of the CAMs that came out of his machine that perhaps they were not engaging any more because they wore down due to their overrunning nature.
As far as I know, Kubota has not issued a PSB stating that the old style CAMS were responsible for PTO failure. The do have a PSB out that says that the old style CAMS were replaced with new non overrunning 'Solid' type CAMS.
Some users have had their dealers replace the PTO CAMS with the new style ones. This requires splitting the tractor and is a major job.
Other users dealers and Kubota have not agreed to do this.
My own personal experience on this is complicated. Kubota initially turned down the CAM replacement request (I made through a dealer where I did nto purchase the tractor)... after a lot of rigamarole I was told that my selling dealer would do it but I do not have any reasonable relationship or trust left in them. Other dealers around here anyway do not prefer to take on warranty work unless they sold the tractor. Kubota in Canada appears to have an unwritten policy that allows this. There is some grey area here as the existence of the old style CAMs is not a sign of imminent failure. If my PTO (or some other part) actually failed under warranty I would be getting the work done at a dealer of my choice as I will not purchase a quart of oil at my selling dealer.... and if I got any hassle about it wrt. warranty coverage I'd fight it. Luckily for me, Kubotas are about the most reliable machines out there ... so chances are I won't be getting anything done under warranty (cross fingers).
There is also the odd report of a PTO not engaging / disengaging as a result of a failure in the cable linkage that controls PTO engagment / disengagement. There is a PSB about this also.
Overall I think that you have to decide whether you want to try to be proactive about some of of these PSBs that are out there and whether your dealer will fix them under warranty for you even if your tractor does not have a problem.
My personal opinion is that if I were to have to do it again, I don't think I would have even tried to get the PTO CAMs changed. It is too major a job - splitting a tractor for something that I don't know 100% really will be a problem. For all I know the main reason Kubota might have changed the CAMs was because of the noise (and this would not surprise me). I would have fought tooth and nail on the valve issue as it was unacceptable to have an inching valve even if this is an 'economy tractor'... plus I pointed this out before I purchased it.
I don't plan on trying to get any PSB applied unless I am actively affected by it or I am convinced that it will imminently affect my tractor. Reality is that there will always be PSBs whether they are from improvements in design or just convenience upgrades. Overall Kubota makes really reliable quality products and it is not worth my time worring about a failure that I may or may not have. If I was running a tiller all the time, I might have pushed further to get my CAMs changed. I might get an external overrunning coupler to prevent the internal one from wearing at all. As it is, I barely let it rachet and I don't use my PTO for over 50% of the tractor hours anyway.
It is upto you as to how you should proceed and how your dealer will accomodate you. I would just let it be unless you run into an actual problem like a broken PTO or a PTO that won't disengage. If it ain't broke, don't fix it! Kubota sells a LOT of these machines and problems (PTO or otherwise) are few and far between as reported on this board. And trust me... if there are problems - they surface right to the top.
Just MHO. Hope my thoughts help you.
