Well, I got my two unts used, so don;t know for sure, but the pumps and valves LOOK like they have not been changed. A hose or two is normal with age though.
One key....... Change the fluid!! Every year I dump it out, and refill with Shell Rotella 15w40. Argee is right. The older tractors had no filter in them. I have checked with my dealer, and they have never heard of a retrofit kit for a older tractor.
One of my projects this winter is making something for my 444. Filter placement is the big problem. There is just not enough room in the older tractors under the hood for a filter. I am planing on mouting it on the side for the dash part of the tractor. About half way down. It will be outside the hood, but seems like it will be out of the way of all the attachments. I will post pictures when I do.