I recently had to replace the rear wiper motor on a 2011 FD hatchback, the wiper was moving very slowly and stalling in places. I obtained a 2nd hand motor to replace it with but found it impossible to pull the wiper arm off the motor shaft. I bought a puller tool, but it wouldn't budge even after tightening up the puller as tight as I dared, and applying penetrating oil, heat, tapping it with a hammer, wiggling the arm. Eventually I resorted to sawing through the shaft, then knocked out what was left of the shaft from the arm. Didn't matter as I was replacing the motor anyway.
It may be advisable to pull the wiper arms off the shafts every couple of years, just to make sure they don't seize on. Apply a smear of anti-seize compound, just to make sure the arm will come off when you really need it to.