The local Fire Dept. has a D7G dozer, serial # 4YB00010. I have a old serial number book but it stops at D7F and my Newer Cat book does not have a listing for a 4YB. What gives with this? I was told it was a 75 model but after finding the serial # plate it says 1982 and delivered in 11-1983. It is supposed to only have 400 hrs. on it. catskinner