White Knight CL797R running fine but no heat?

10yr-old dryer running fine until yesterday when I noticed there was no heat. I've cleaned the condensor thingy and given it a kick - that's the extent of my technical skills. Ok, I've taken the top off too and can see the drum and a circuit board, which all looks fine (how does so much dust get in there?).

I've taken the screws off the the bulgy metal thing at the back, but it won't budge. I suspect it may be holding the drum in place, so I'm not doing anything else without further advice.

Having surfed around, I'm leaning towards a thermostat failure (hopefully nothing more drastic). There's one on eBay for £13 odd, but, assuming that's what I need and it's a good price (it is new), how do I go about fitting it. I'm sure I have a fair chance of success with the right guidance.

Thanks in advance. :-)