The roof motor can be replaced without taking off the roof. The pump motor itself is like $65 dollars on Amazon, all you need to do is remove the old bracket/pump and put it on the new one.
I just did one last summer, took 1hr.
https://www.amazon.ca/DIPMOTOR-Conve...zcF9hdGY&psc=1
The E85 Z4 2.5 and 3.0 i/Si is by far my fav convertible. The motor is a real gem, and the car is classy as hell.
Srippy and sporty but definitely on the soft side compared to a real sports car. Muted steering, but the hood doubles as a mirror.