Dunno about removing marks or using ultrasonic cleaning, but there have been numerous reports from very trustworthy people that PCGS has dipped coins, and I have, once, seen PCGS admit in print that they will dip some coins in acetone before slabbing them - not only without permission from the owners, but without even notifying them.
I think the coin would be worth more in the holder. This would be the case where someone does buy the slab just to put into a collection to show people that you never buy the slab That being said that has got to be one of the ugliest 31-S I've ever seen put up in plastic. I'm not sure what the grader was thinking that day.
Yes I do have proof. These were valuable coins and I had photographed them before submission. I had to return them three times to PCGS for their "observation" and photographed them each time. They refused to admit that they had doctored the coins and had actually dropped one of them ( apparently on the floor judging from drag marks on the devices ). Arrogance and deceit!
Remember when you payed a little more money for a PCGS coin than an NGC coin. Used to be they were stricter in their grading . With the fake going around and I have heard nothing fromPCGS about damage control. Why Pay More?