I have a 1999 JD 455 with approximately 750 hours of use on the hour meter and a 54 inch Heavy Duty mower deck. I have always kept the mower and the deck serviced, and the underneath side of the deck cleaned out, and painted to prevent rust. Apparently, the input seal on the mower deck gear box must have failed at some point, causing a failure of the gear box.
The Box was completely dry of oil, and it appears that a bearing has failed. The new replacement gear box, was a perfect replacement, and it seems to be working well.
It is sad that John Deere does not offer replacement parts, but perhaps the clearance tolerances are so close, they do not want to run the risk of failure due to improper assembly. I did purchase new seals, and plugs in the event I am able to find replacement bearings for the old one, therefore, I will have a replacement ready should the need arise.
This dealer has the best price of all! Local prices were $200 to $300 higher!