Brake master cylinder rubber cap melting (1 Viewer)

[middlecalf]

On the plastic cupped MCs, why is my rubber cap “melting?” It‘s sticky and black stains the hands readily. DOT 3 used only, and this is the only time in five AISIN MC’s that I’ve noticed this happening. SBC with Carter AFB, no signs of fuel leaking but there is the usual hot engine evapo out of the carb, but first time in 13yrs I’ve run this rig that this meltdown has occurred. Thoughts?

 

[B y r o n]

Maybe the cap is just getting old. A friend who lives in Idaho says it has been pretty warm this year, maybe that is contributing.