I have had a 4700 swather. I had to rebuild the whole hydrostatic pump which was about $10K, after 2 wheel motors, 2 gears and hydro pump etc... You have to make sure the hydro is working properly. The swather should go fast when in full forward position, I never tested mine for full forward until I had brought it home and it went quite slow in full forward position. I only used it one season before it cratered.
There is a gear housing between the motor and hydrostatic pump which uses it's own gear oil, which you can see with a sight glass from underneath the swather. You just have to make sure this gearbox has oil in the sight glass and the hydrostatic pump always has the right amount of oil. If it has been looked after it should be a good swather. Just remember the hydrostatic pump runs everything, the reel, canvasses, and wheel motors. Check the steering linkage underneath also, they can get loose.
Hope this helps a little. I realize there is going to be wear and tear after the years but the hydro pump and gearbox are really important to check. Good luck.
Check the frame over really close for cracks. I have seen a few that split between the cab and hood. I had one crack badly at the top of the legs on the front. Hydro parts are hard to come by, but other stuff like the planetaries and canvas drive motors are available through the original suppliers. The splitter box gears are no longer available, but if they are in good shape and you keep the oil at the proper level they should be fine.