Both the blower and the regulator are Specially priced (bg) for the 129 car. The regulator comes with the blower if I remember correctly and the most common reason for regulator failure is high current loads due to problems with the blower motor itself. I would recommend replacing them both as a unit if I'm right about the reg coming with the blower.
Bosch Master, ASE Master, L1
33 years MB technician