Crank sensor fault code :(

I've got a problem with my vw golf tdi
Done a scan and got a fault code for crank sensor, replaced this and the problem went away,
Two maybe three months later of my car running smooth and pulling with loads of torque,
The same code has come back again but now it won't start at all,
Also getting the crazy bouncing rpm needle when trying to start?

I've tested the resistance of the crank sensor and that seems to be ok (spec from auto data)
Also tested to make sure I'm getting power to the plug that feeds the crank sensor which is ok.

I'm getting the bouncing needle again when trying to fire her up.

Btw the way the code I'm getting is crank sensor implausible!

Also noticed ive got a bit of a leaking tandum pump.


Things I've tested.

Resistance of injector loom
Power to ecu
power to glow plugs
power to injector loom
Resistance of crank sensor.

Changed 109 relay
changed fuel pump relay
Changed key ignition barrel

Cleaned all earth points.
Checked there's fuel getting to the fuel filter
Checked the lift pump is working and priming to front of the car.

If I remember anything else I've done I will post.

I'm really hoping somebody has a pointer to help me out with this,
Other than put it into a vw garage as they know best! Which isn't always the case haha