Tyre pressure monitors

[Chattonmill]

One of the tyre pressure monitors on my E55 has snapped at the top.
The system seem to comprise of two bits, the bit that attaches to the wheel on the inside, then the bit that has a rounded bottom that sit in there and houses the valve.
The bit that has snapped is the thread where the cap goes on, leaving the valve head partially exposed.
Can I just replace this part or do I have to replace the whole thing.

 

[npuk]

The valve kit and the TPM sensor are sold seperate so you should be able to change just the valve. Alloywheelsdirect sell them.