Hi, yes, the circuit board with the four contacts sticking upwards has to be unsoldered from the three pins that can be seen across the wider end of the circuit board, these three pins are the legs of the MOSFET. Once the solder has been drawn off the three pins and that end of the circuit board is loose on the pins/legs it can be unclipped and will swing up but will still be held by the wires from the thermal fuse. The screw holding the fuse and MOSFET will then be visible.
I used a soldering iron and a solder-sucker to do this when I took my failed unit to pieces. The paste that you will see beneath the MOSFET and the fuse is a special thermal condtuctive paste to ensure very good contact with the heatsink.
I'd not say you were a mug for buying a new one, I'm an electronics engineer and taking this sort of thing apart is what I used to do; if you're not familiar with soldering things like this there are pitfalls. Don't let the legs of the MOSFET get too hot when soldering, you can damage the component as you fit it and heavy use of a soldering iron on the thernal fuse can blow it as you fix it in!
Have you asked at any breaker's yards for a used one?
