Replace the power button lever and check the mechanism is working.

We need a layer of something like thin plastic to stop sealant squeezing into the mechanism and gumming it all up. I used a bit of bread-bag.

Cut a bit big enough to protect the parts of the mechanism that will be located just inside the hole in the casing with a good margin around for sealant to squeeze inside and spread a bit.

Use a tiny bit of sellotape to hold the cellophane in place around the mechanism. I mustn't slide down as you push it in.