The rear wiper used to stop half way through the sweep…….

I bought a motor from a 2008 fiesta mk6 with good carbon bushes for £12, you can swap out the motor from the fiesta mechanism housing.
I used a magnet to hold the metal fixing plates whilst removing the motor screw. Do this to both sides and pull the motor free. (you may need to remove the mechanism backing plate first for screws to be removed). The carbon motor bushes on the FL2 unit had perished, hence a weak performance and the arm sticking.

You can either remove the plastic bush housing and motor from a compatible donor and transfer it to the FL2 mechanism. Or see if you can source new bushes.

Please note: the shaft on the fiesta unit that passes through the rear window is too short for the FL2. So only swapping out the bush housing and motor is key. Fit the bush housing to the motor first, using a thin bladed tool to manipulate the bushes into place. Fit motor into the rotary mechanism first. Once securely in place, hold the screw axel that meshes with the plastic wheel tightly before fitting the motor cover…… This is because if you just try and put the motor cover back on without holding the gear shaft, the motor whips back in the motor cover, attracted by the magnets… . The bush housing stays on the mechanism and your back to square one. Annoying…

It’s so much easier to attach the bush housing to the Motor first before adding the case.
Finally use the magnet again to hold the metal plates then secure the motor with the two screws. Using the magnet trick is like using a really useful set of hands whilst you locate and tighten the screw.

Refit motor and check it works before putting everything else back.

So the bottom line is that it was the carbon brushes wearing out. Plain and simple.

Hope this helps.