The 'end-caps' are the hard plastic that bolt to the aluminum master channel.
The soft PU bumpers are screwed to through the end cap to the master channel to protect frames from the brush.
If you are tearing them, check your technique as you may be applying unnecessary force against the frames.
When replacing, be careful to no over-tighten the screws for the bumpers.
1 x LEFT / RIGHT SET of whichever option you choose
1 x TOOL for SCREW / BOLT
1 x SET REPLACEMENT SCREWS for bumpers