[_Cosmic_]

Go slowly and cautiously all the time.

We should now be able to inspect the inside of the unit.
With the grill facing downwards towards the bench, take off the brown plastic half of the case. Hopefully you will be faced with a layer of fibre wadding or if you are unlucky, a mass of decomposing foam that will turn into powder as soon as you touch it or disturb it. Both mine were wadding.

carefully feel off the white wadding with a pair of tweezers and turn it over and place it out of the way. Yu are now confronted with a shiny surface. This is the mylon sheet. It is rather special in that the upper surface is conductive. Attached to the conductive (upper) surface is the very thin copper-coloured conductive film which brings the signal from the output transformer to the mylon sheet surface.

Do not try to remove the sheet from the metal grill in case you damage it. It will be probably be fastened down anyhow.

At this stage, if it hasn't already moved, with your tweezers, carefully remove the coper-coloured film strip and inspect it. It will be tarnished. I used a small amount of Brasso on a cotton bud to gently (stroking gently one way) clean the strip to ensure it will make a nice clean contact when you reassemble it. Rub one way in case you damage the film on the back stroke and it rucks up. Perhaps try a little isopropyl alcohol if you have any in place of the Brasso. I use it for everything!

We have now hopefully eliminated one possible cause of the tweeter to fail.

Take photos of everything as you go along. If case you don't, you can always come back to look at mine.
You have done well so far. We are now going to inspect the wadding so you know what to expect and discuss what causes these units fail.

I posted some images so you can refer to them again.