Hi Thom.
this is the diagram for the spoiler circuit.
as you can see, it consists of two relays that converts polarity to the motor based on the up and down function.
the relays are located on the fuse/relay box in the rear trunk (driver side), and activated by the cluster. so if your speed gauge works fine, your speed sensor is fine as well.
there is a small microswitch located on the spoiler mechanism, that indicates to the cluster the position of the spoiler. you might want to have a look at that.
but before you do anything, i suggest you give the spoiler pistons a good clean , and try to gently push it down when another person is pressing the spoiler switch on the kick panel.
good luck.