300 pto rebuild

My 300 Farmall has a weak pto. If I put on something that requires a lot of power it slows down and almost stops. I have adjusted it as the shop manual says and it still slips. I am pretty sure the bands are shot. I have had the pto unit off before to replace the seal between the rear end and pto. How much of a job is it to pull apart the pto unit and replace the bands ?

he linkage on well used PTOs on the 300-350 series become dysfunctional after years of use.
Two suggestions:
Make very sure there is no lost motion in the hand lever pivot and rod mechanism. Be certain the hand lever moves the PTO lever from the middle both ways.
Adjust it like this, after there is no play in links.
Move the lever exactly half way between the locked on position and locked off position (little flipper catch on lever. Bungy if needed to hold this spot
Take off the little dome metal cover from the adjust screws.
Loosen the jamb nut, and tighten the front (away from you) screw until it is just a bit tighter than the point at which it begins to feel tighter as it is screwed in (maybe a eighth turn) then back it off until the PTO shaft will turn with least drag (about 3/4 turn out) and tighten the lock nut while holding the adjuster.
Do the same for the closer adjuster.
If the screws go into the jamb nuts and get flush with the top surface of the nut, the bands are probably worn out, and may be operational for a while, but plan on a rebuild.
Now (tractor off) push the the lever down toward the brake footplate. As it goes down, it should get harder to push when it is about 4" (or so) away from fully OFF. and be noticeably harder to push for the last inch, but not real hard. (this is the brake band tightening on the drum in the PTO unit.
Then pull it up and do the same feel.
The ON position should feel the same way.
The shaft should turn pretty free when the lever is half way, and not at all when in either ON, or OFF. (tractor shut off)
If it slips now, it needs a rebuild. JimN