I own an older home that has wall registers. A few years ago we had our ducts cleaned and it was really difficult to re-attatch the vents to the wall as the area where the screws go in crumbled. It's time to have the ducts cleaned again, and I'm worried about taking the vents off to do this as I won't be able to get them back on.

Are there any suggestions as to what I do to screw the vent back on....or is there another way to go that isn't going to damage the wall? If we screw into a new area in the wall, I assume I'll just cause that to crumble.

Help!