For him it maybe normal. Some gliders have environmental stress, meaning even the slightest change in the cage will make them over groom. My Simon is one of them, he has 3 cage mates, toys, out of cage time, good diet, good sized cage and is a constant over groomer, mainly above the eyes as well. When I got him he was single and had been single for 4 yrs I had hopes that with a cage mate it would stop. It's not as drastic now, 3 yrs later , but still present.
For him I don't change much in the cage, the toys stay in the same place, the same toys stay in the cage, I only add a new toy once in a while to minimize his stress levels. He was used to a small cage with nothing in it, going from that to a big cage with lots in it was a big change for him.
There are mannnnnnnnnny reasons for over grooming, the hard part is figuring out what the triggers are for that specific glider. If you make to many changes to quickly, you won't see which one triggered it.
Another big environmental change ( going to new people in a new house and another new glider scent) may stir it up again, so yes I would let the new owners know it's an existing thing with him and different ways they can help him ( like not changing to much to quickly, removing a fav toy etc ) Simon has a tractor that is always in the cage it's his fav and when I take it out any longer than to clean it he stresses.