If you ask me the lube just accelerated the problem. The root cause remains that you have a part secured with only a friction fit, in a setting where if that friction fit fails you have a a critical failure of the system. Friction fits can be very strong when properly established between appropriate materials, but this was not that. This was a cheap plastic cover made to be a bit too small over the metal lever. Over time with heat, sand/dirt, cold, pressure, vibration, etc. cycles, this was going to fall off regardless.