The dark side of Shugborough

I think, everyone who have visited Shugborough Hall with the sole purpose to see the famous Shepherds Monument, ended up a bit disappointed about it's unclean, neglected state. It has never changed for more than 10 years of my Shugborough research, and it was like that probably years before that. It is a Grade II listed monument and it should be treated appropriately according to the British law. But it's not. Why? My guess is that it is done on purpose, so the people would not be able to see many things on Monument or confuse them with dirt or something else. Just have a look here to see what I mean  As you can see, there is a triangular shape stain on the marble, but it does not look natural because there are few different pieces of marble involved here and the stain sharply ends up just above the OUOSVAVV letters. If it is not natural, then it is artificially made. Most probably the stain was left by a fluid and that would explain how it appears on different pieces of Monume...