That is exactly what he was talking about, and I also agree with his prognosis. The screen is not sitting properly in its place, likely because its place is tweaked.
You make a very good point, one that I had not considered. The focusing screen is frameless, therefore a new screen would likely do no good. It would almost have to be the seating in the camera body. Best have a pro look at it, if it's something you care about. Personally, that sort of thing would drive me nuts, and I would be delighted to spend whatever (within reason) getting it fixed.
Right now in Spain they're holding the Running of the Bulls,
followed by the Soiling of the Pants, and the Burying of the Idiots.