Brian, thanks for the quick reply.

I called Steve first, very friendly & helpful person. Unfortunately, he told me they or no one else have the alignment tools necessary to check a Mamiya.
But, he gave the me the contact info for their repair department back in New York. I just spoke with a guy there who was also quite helpful and recommended shipping it to them to check and repair.

For reference, in case someone else searches for this (and perhaps this forum has already covered this a thousand times before):

Mamiya's number is: 914-347-3300
and
he said the issue could not only be the mirror or focusing glass, but could also be the lens, back, or even the insert.