Raytheon ST60 Faulty Readings

[Marauder]

I have a 10 year old Hunter that has a Raytheon ST60 wind instrument fitted as standard. Since owning the boat for the last 6 months, the readout has given consistently wrong information. The wind direction is approx 170-180 degrees out and wind speed approx 10kts out. I have tried to calibrate it as per instruction book (2 circles and wait for the beep) but can not even get it into this mode. Everything appears to spin freely at the top of the mast, and point in the right direction, and alters as speed and direction changes but readout is definetly wrong. Speed is always on the high side, both in apparent and true settings. Not being a person for heights, wondering is it worthwhile paying a rigger to check connections at the top of mast or is this a throw away type item. The readout on the gauge is the same that passes through to the Raytheon Any suggestions appreciated.