I recently bought a grey B7001 and I assume Kubota still use similar technology. The guy in the local spare parts dealer said they are selling alot of plastic tanks in Aust. People leave the tractor in the sun with a half full tank. Damage from the suns radiation and heat/pressure build up split the tanks down the seam. - solution - Keep tank full of diesel and don't leave tractor in the sun. Fades the paintwork anyway. I get the feeling that these tanks have a limited life span and are not UV stabilised plastic.