Driver's seat motors/adjustment

Hi all,

My recently-purchased 2008 3.0 TDI has an issue with the front seat motor. I can lower or raise the seat at the rear, using the lever/switch thingy on the side of the seat base... but - while it makes a noise - the motor fails to raise the squab at the front of the seat.

As a result, the front is as low as it will go... OK for a short driver but less than ideal as I'm 6ft6.

The passenger seat squab happily goes up and down, so I know that the driver's one should too.

Anyone got any hints as to what I should be looking for if I take the seat out?

Is it cable-operated? Gear wheels? What is likely to have come apart, to prevent the seat squab from moving?

Any/all bright ideas gratefully appreciated...