yeah to my knowledge they are still using plastic gear, even the new replacement. On some engines, yeah they switched to metal, but you also had to change the crank spur gear, meaning pull the crankshaft out. Kawasaki Mules were notorious for it, on the KAF620's, pre A5 models (pre 1999). 99- were all metal gears, and they made a little more noise. Those are FD620D engines; and some of them were also used on generators and mowers, but to my knowledge, Kubota didn't use the 620. John Deere did, 425 and 445, among others. Did many a plastic gear replacement on those 425's. Likely a hundred or thereabouts. I know it was a bunch of them. Then about 50 Mules over the years.
.25mm is fine. 25mm is a shade less than one inch. Plugs .025" is fine. Yeah the manuals are weird, all of the Kubota manuals are. They are written in Jinglish I think.