Skoda Octavia - Central locking - boot - Dave.B

I have just bought a 53 reg skoda octavia with 280,000 miles on the clock.

The boot will not lock on central locking, and the lock barrel is seized from road grime. On inspection it appeared that the servo was broken, as it was not moving when the lock was operated. I have ordered and fitted a new one, however the problem is not solved. Any idea where the fault might be and how to rectify it? Not looking at using a dealer/garage as the car was only £750.