Speedometer not at Zero

^^^ yes that is true. The spring is anchored on to the shaft and its tension is set with a rod that the other end of the spring goes through. The spring rod is secured in place by a small nut. It is possible the nut came loose enough to relieve the tension on the spring. I would think it a very rare occurrence that would happen though but certainly it is possible.

It is costly to send a speedo out to be repaired and think the most cost effective outcome would probably be to replace the speedo assembly. Or go into a repair with that in mind and try fixing it yourself depending on your abilities.