drivers side seat height adjustment not working forward and backward works fine so whats wrong

Yep as Tom said these seats do have multiple motors and theyre known to go bad.

But what your both forgetting is that these are mercedes benz seat motors, they just don't break... I'd put my money on it being a faulty seat control switch panel or a relay, the cars 13 years old so it;s about time something like that broke.

Needs a new switch