Weller EC1201A Soldering Iron - intermittent temp sensor

[brian_mk]

The iron works normally for days or weeks but there seems to be an intermittent fault with the temp sensor.
When this happens, the temp indicated on the base unit is all over the place and the iron does not heat properly.
When in this state, if I pull the soldering iron plug from the base unit and check the resistance of the temp sensor pins, it measures a few killohms.
The measured resistance is not stable but fluctuates. It should be a steady 40 Ohms or so.
If I tap the sensor a few times the resistance usually goes back to normal and the iron works again.
I am pretty sure it's not the cable or the soldered connections to the sensor.
It looks like an intermittent connection inside the sensor itself.
They are still available (Part No. EC229A) but are expensive to replace (around £80 or more).

I don't know how the sensor works. Does it use a platinum or similar resitance wire?
A wire is visible inside a short glass tube (looks rather like a glass fuse). See attached image.
Could it be the connection between the wire and the external solder terminals?
Does anyone know if they can be repaired?