I think the vibration motor in the FP2 bottom module can be replaced with limited effort, but I cannot provide details other than iFixit’s teardown (Step 10, photo 2):
If you are lucky, you might even be close to one of Italy’s two Fairphone Angels:
Last but not least, I think it is very unusual to find a hardware defect in the vibration motor of the FP2. Have you checked it with Settings > System > Maintenance > Checkup ?