I recently noticed that coolant leak on driver side under the carpet. I checked radiator there was no coolant left after a minor heat up.

I been told that heater core developed a leak. I had little chat with local mechanic about replacing core labour and cost etc, and he quoted more than the car value. I think it will be only worth if I can replace core by myself. I am reasonable good in DIY tasks, I would like to replace myself, if some one gives me instructions to complete this task or link to the web site. Other suggestion or guides will receive with big thanks

I will appreciate your input in this matter.

Car details are as follow:
Mitsubishi Space Wagon, 2 GLXi, petrol, UK model (right hand drive), manual transmission, registered 1994.