Simon,
I can't imagine that this is all that likely there as it's probably drier there, but on my 1200s I have found rust down inside the scuttle was usually the cause of big leaks. You get
all old leaves and stuff collect in there and it stays damp all the time. You can usually see any rust from under the dash, although sometimes it can be hard to spot. It can be a
pain in the arse to fix too
Eddie