Considering that the motor seems to be fine, based on the clicking I would try this:
Look under the seat and see if you can locate the froward.backward motor (should look like a silver cylinder). Take a hammer and give it a few taps. Not as hard as if you were driving in a nail, but hard enough to hurt ones finger if you'd miss

. if the seat moves after tapping you have the drive shaft gear issue.
This is a very common problem in early maximas/ i30s and i35s, there's a chance early M's were sharing same parts.
Let us know.