Control arm bumpers

[eric8]

Was cleaning off built up grease and gunk from my lower control arms (77 C10) and noticed a slit in both sides out towards the ball joint area. I thought "hmmm....looks like something should go there." Sure enough, the parts manual indicates a rubber bumper resides in the groove.

Both bumpers are present on the upper control arms. Truck is very original. Just curious, is there a reason they could have been removed? Maybe just rotted away? Has anyone else found the lowers missing? Just curious why they may have disappeared.