I have only seen one mail padlock of this type ever posted on eBay. As you can see, this is a very nice one, at least it cleaned up well.
really nice old postal padlock that works great & has a nice working key... the markings that are on the lock are pretty darn sharp... this was a high security padlock in its day & still is. - eBay
It seems that many lock collectors look down on cleaning locks in the same way that you don't clean collectable coins as it reduces the value of them. I am not sure how the value might be effected when it comes to locks, as a piece cleaned like this one is surely much more interesting to look at if you decide to show it off. I clean most of the locks I have, after al, brass was made to be polished!
This lock sold for $104.47 (Plus $9.50 in shipping)-----