How to fix faulty 2004 Mitsu Galant Speedometer?

Hi I just had my heating fixed on my 2004 Mitsubishi Galant. The mechanic had to remove the dashboard and replace 3 parts (heater control valve, blend door actuator and heater core). The heating works now, but my speedometer cluster is messed up. The RPM needle works, and so do the temperature and fuel tank indicators. However, the temperature indicator is slightly lower than where it should be, and the fuel tank needle is slightly higher than it should be. The speedometer needle is completely messed up and starts very low within the cluster, much below the 0 mark. It then picks up and goes to a maximum of 40 kph. It however doesn't pick up in a normal fashion. It doesnt seem to be just un-aligned and off the 0 position but a little weird in general. I am going to give it back to my mechanic soon to get it fixed but I thought I'd get some advice from you anyways. What could be the problem? My mechanic told me to open up the cluster on my dash and try to re-align the needle by hand (while the car is off), which I did, but as soon as I turned the car back on, the needle went haywire and fell back below the mark. Please advise, thanks!

Waqas