as it happened to both cube I would suggest to check your PSU first
I'm fascinated to know how you think the PSU could make the fuse melt?
Not had the top off either cube yet but wondering if there is something that gets very hot, close to the fuse socket, between the fuse and power sockets. A heat sink perhaps? It was that side of the fuse plastic that was in worst condition.
Will have 30A and 40A replacement fuses on hand soon so will experiment. May also have urge to have a look inside.
Either way, if I find anything, I will update here.
PS. Anyone have a pointer to pics of naked cube?
If not, and I do get my screwdriver out, I will take lots of pics!