That comment just means I couldn't pull or work it off so I took the die grinder and ground the side of the arm off. Once there was some of the arm attachment ground off I just pulled it off. One doesn't have to destroy the spline on the motor shaft, just get down to it. The arm head is pot-metal, which explains the problem.
Don't forget to protect the gel coat surface whilst you're grinding away.
The replacement wiper motors swing angle could be set to a variety of angles between 40 deg up to 90 deg.
Boris