Yup that's the bit on the shift shaft that breaks off that I mentioned in my post. Usually happens when the shift lever gets a good wack from a rock or something in a fall. Proper pain in the a*** job. Glad you found the problem.
PS, I called it! Been there done it my friend. I feel your pain. While you have the motor apart take the opportunity to change crank seals and output shaft seals etc.
Good luck.