Hi mr Burns,
This thread shows how to dissasemble a Sky.
The red arrow pointing towards the cap in the last picture…you can see the join between the cap and the center housing with the ultrasonic sensors has some gaps. There is a rubber seal in that join to be careful of when you insert a thin stanly knife style device to prize the lid slightly wider to disengage 4 little ridges which normally hold it in place. But when doing that be careful not to let the two parts seperate very far as there is a ribbon cable joining both components which can break if stretched.
While I have disassembled a Sky I have never repaired one.
But sometimes a failed sky given a rest inside for a few months next time I try it comes back to life.
Cheers Ian 