I walked about 300 meters of Y1 this week and took some photos of the beam tube insulation.
Between ports 2 and 3 (a distance of 250m) I counted 35 holes in the insulation. Virtually all of these holes were at taped joints between insulation wraps. These joints occur every 4 feet.
So of 800 taped joints I saw 35 which were violated by rodents. There may have been a few more on the backside of the tube. The photos in this report show some of the holes, some of the "good" taped joints, and some views of the uninsulated bellows regions.
Thursday I looked into X1 and X2 (but not Y2) specifically to see if the bellows are insulated. It looks like they are so Y1 may be unique in this regard. However, the insulation is pretty ragged and will need to be scrapped.