If the manual switch works at the fuse panel, (should go up fully automatic with one tap in the up direction and then you have to hold continually to fully retract), and you don't have a failure light on the cluster, the fuses and solenoids are working. I suspect there may be a signal from the cluster at 75 mph for up and 50 mph for down that is causing issue and not the spoiler. If the spoiler fails to extend after 75 mph and no failure light is present, than you are not getting a signal from cluster. Manually extend the spoiler with the manual switch, then drive the car over 50 mph, slow down and check if the spoiler retracts on its own. If that works, the signal to extend is not being sent. You may be able to do a reboot battery disconnect (negative only) for 30 minutes or so, then reconnect, wait 20 minutes before touching anything and see if it helps. otherwise someone more competent in cluster signals might be able to trouble shoot it for you. Due to the expense of the spoiler assembly it is definitely worth fixing. Mine was micro switch failure inside spoiler assembly. PITA but I had failure light at the cluster. You could always just extend it and drive it like that... I couldn't
good luck.
MY2001S