When I reinstalled my scope on the bench shelf, I noticed that the combination of my bench power supply, Agilent and Rigol scopes all next to each other were making quite a bit of heat. Plus the shelves are not ventilated, they are solid wood. The heat was building up. This may have led to the death of the scope eh?
I installed 100mm computer fans at each end of the row of equipment so it's blowing fresh air behind the whole group of equipment. It's made a very big difference, subjectively anyway.