[Deleeh]

Interesting. I've never heard of flux that just brushed off. Learn something new every day, I guess.

Nylon tends to stretch over time and gets brittle. So it's not a good choice for a mounting screw.

All the transistors need thermal pads between them and the chassis or the metal of the transistor (which is electrically connected to the middle pin of the transistor) will short to the chassis and make bad things happen.
The two TO-220 package devices need a shoulder washer (that white insulator) in addition to the thermal pad or the mounting screw will cause the transistor to be connected to the chassis.
The four TO-126 package devices don't need a shoulder washer as the mounting screw never touches the metal in the device. I'm usually kind and put a flat washer between the nut and the transistor just to put the pressure on a larger area.
It requires surprisingly little torque to get a good amount of pressure on the thermal pads. The recommendation is generally 0.5 Nm which is maybe a quarter to half a turn beyond finger tight.

Tom

Hello Tom,
My wife is ordering me a set.Doesn't cost the earth and shipping is free.On Aliexpress they wanted additional shipping.
I think I lost one or it was never there.
I found the other one in the hoover earlier and put it in, but I couldn't find the second one.
Hooray for the Dyson hoover.

The mats are all there, I taped them up a bit so they don't slip when I put them together.
Of course I wondered what happened to the others, if they needed one of the plastic discs.
I would have put some in if you hadn't said anything to be sure.

Yes, the toothbrush is actually quite good, you can get everywhere and it is soft so as not to damage the circuit board, I thought.
A splash of alcohol also helped and I only soldered after it had evaporated.
You have to scrub a bit but it works. It was more of an emergency solution.

And thanks again for the reply,.