1. MF165 PTO problems 2. what is the petal by right heel?

1. new to me 165 gas. Was mowing today, live PTO was working fine to start, then it started to grind when I tried to engage it. When the tractor was off it would engage, and I could start it with it engaged and the thing worked fine. I have a MF 202 that did that and I did then clutch adjustment to it and it fixed the problem. Figured I had to do this on the 165. However, later it was failing to engage at all no matter what I did, but the ground speed PTO did engage. When I put it up for the day I tried to engage it and it did with no difficulty. Any ideas?

2. What is the pedal down by my right heel? Looks like it hooks into the axle housing.

Its quite possible that the lining on one side of the PTO plate has broken free. It usually falls and get trapped between the good part of the clutch plate and the pressure plate. On one side you have two thicknesses of lining and on the other, one. The pedal will feel much the same
but will not allow the plate to stop turning when disengaged. The loose bit will move around so there may be times when you can engage it.
The pedal at your right heel is the 'differential lock pedal'. This pedal should be completely free to return to the 'up' position. When one wheel starts to slip the pedal can be pressed to lock the rear wheels together and increase traction. It can be used in a shallow steering curve but is only really for straight ahead work. When engaged the pedal will remain in place. If it does not free of is own accord steer a little to the left and right and it should disengage. It must not be engaged at high speed and likewise when turning corners particularly on tarmac or concrete. Doing so can cause major damage in the transmission. When engaged., the tractor will always try to steer straight ahead. Don't try and fight it.
DavidP, South Wales