Rear wiper motor is stuck half way

Corrosion in the wiper arm shaft is very common on these and will prevent the arm from going back to the park position. Remove the wiper arm 13mm nut and disassemble the shaft from the window. after removing the wiper arm, remove the circlip and the 22mm nut holding the shaft assembly to the glass on the outside and remove the 2 11mm nuts from the inside then you can take this assembly to a bench and thoroughly clean and spray with wd40 or equivalent. I included some pictures of the outside and inside views of the wiper shaft assembly.