Welcome to the forum .
Seems strange they can tell you how long the part will last. They must have a good crystal ball, dealers are good at scaring us into parting with money.
Does the motor make a noise? Does it take a long time, to fold down or go back up? If the part is greased up doesn't mean its bad all of the time.
What has the person or dealership you bought it from said, about rectifying the parts.