Most of the classic Tek scopes have a fan, and most of these fans are mounted on the rear panel. In the typical arrangement, there is a yoke attached to the rear panel, and the fan motor is attached to this yoke using cylindrical rubber shock mounts. Typically these are 1/2" (12.5mm) in diameter and 1/2" (12.5mm) or 5/8" (15.8mm) in height. Tektronix part #348-008 is a typical example. They have 8-32 threaded rods sticking out at both ends. The purpose of these rubber shock mounts is to prevent the vibrations from the motor from vibrating the whole scope.
The original rubber shock mounts eventually get dry and brittle and can break, leaving the fan completely unsupported, inoperable, and, in transit, the fan can move slam into delicate components inside the scope, possibly causing damage. A temporary remedy is to glue the shock mounts back together. Epoxy works for this purpose. A permanent solution is to remove the metal pieces from the shock mount, and to make a new one using plastic hose. The two metal threaded pieces should be spaced apart the correct distance by the hose, and the assembly can be epoxied back together.
Another method used by some is to go to McMaster-Carr @ www.mcmaster.com and buy the vibration-damping sandwich mounts with the part number 9376K17 and these should be a great fit.