The seats on the three Kubotas I've had (B7500, L3200 & L4240) all wanted to dump me forward. The first two were made worse because of the slippery plastic seat cover. It wasn't quite as bad on the L4240 because of the upholstered seat.
The B7500 was just a bit small for comfort with regard to legroom. To solve two problems at the same time I fabbed up a set of mounting channels that were taller in the front than they were in the rear. That raised my whole body and provided more legroom at the same time it cancelled the forward cant of the seat.
For the L3200 I spaced the front of the seat up with washers to make it higher. That didn't solve the problem entirely but it helped and I was too lazy to make another attempt.
Wanting to make sure there was more adjustment than with the washers I used on the L3200, I went a step further on the L4240. A quick trip to the hardware store for a couple longer bolts with the same pitch as the factory bolts, a few nuts and washers fixed it nicely. Picture below. I ran the bolts up from the bottom. The multiple nuts allow for adjustment.
