I believe the problem is the little silicon piece under the spacebar, its the one that completes the contact between the key and the sensor when pressed, before buying a new keyboard, just give it a try. take out the space key with a thin knife by inserting it in one of the corners and then pulling up. if done gently, it shouldnt be a problem. once thats done, put the little silicon thing back on the sensor and try pressing it with your finger(the silicon piece), if it works then thats great, otherwise i guess you'll have to replace the keyboard sensor.
Thanks for the info, I'm definitely going to take a look. However, why does it need to be a Core 2 Duo MacBook? Mine is an original Core Duo model. Would that make a difference?