My HA 114 was made in 1990, so I don't know how the design compares to yours. I did have the same problem and I fixed it very easily. I cut some thin strips from a plastic milk jug and slid them into place. It worked perfectly and has held up for over 15 years.
The rubber band idea is OK for a quick fix, but I wouldn't just leave it at that for the long haul. That would be, as we say in the software business, a hack.