From when I purchased by B3350HSDC 11/07, I have done everything according to the owner's manual, (I have the shop manual too). Used the correct oil (CJ4 rated - IIRC, synthetic for turbo-diesel) at the recommended engine hours and good fresh fuel. On start up, I back off the key to the glow plug position for a few seconds until the engine smooths. The tractor is stored in a shed at no lower than 48 F, I minimize run time below 2100. And I keep track of regen cycles, which for the past few years have rapidly decreased in interval time into the single digits, ending at 4 hours with a new DPF filter and sensors at almost 790 engine hours.
The dealer said the B3350 and the ZD1511 are the only models they see with systemic DPF issues. They share an outdated design using mechanical fuel injection instead of common rail, and that is believed to be a big part of the problem.
I talked to
https://www.kubotaengine.com/parts-service/genuine-kubota-parts/dpf-cleaning-program/
They clean DPF's on "non-captive" Kubota engines, but not on my little tractor. Those DPF cores unbolt to be cleaned of the built up ash residue that is left over from the burnt particulate after regen.
To date and through my ownership, I've had only one regen issue. That was after one computer update where they changed the default setting of Regen button that originally you would have to push each time you started the tractor to enable automatic regen (the light would be on). After that update, you would ONLY push that button to prevent an automatic regen. They didn't tell me that, so I went on tractoring with auto regens disabled until it made me do a parked regen. That's when I found out about the "swap". There have been no other regen related problems like so many have experienced.
The problem is with the design, not with this, or all the other operators who are treating their B3350's right and still facing DPF related issues.