Pentax 645N shutter dial replacement

[Pupfish]

My P645N is almost the perfect 645 film camera. That said, the shutter speed dial popped off for the second time, and now needs replaced as I've lost the center release button. I see these shutter dial assemblies are available new off eBay, but it's not obvious whether the camera needs disassembled to replace it. Anyone know?

 

[John Koehrer]

Naw, it's one of the last things installed.

 

[Kendra]

Do you know if there is supposed to be a spring in the shutter? I had a friend borrow my 645nii and he returned it with the dial and the button but it seems to me there should be a spring. I haven't been able to find an answer.