Just heard about your museum's woes today, sorry I don't know any of you, but it must be soul destroying, you have my sympathy. As a one time operator, I once similarly lost half my operational fleet through the antics of a few vandals which got out of hand.
The North / South thing you have to contend with is totally lost on me I'm afraid, and even more so where a collection of inanimate objects are concerned. I find it difficult to believe that someone would travel all those miles to seek out a few buses which once served in 'The North' simply to destroy them. Usually the perpetrators of such a crime would claim 'ownership' of their 'work', or else, what's the point in doing it if no one knows who or why?
Martyn.