Brake boil over

Because they’re just cheap plastic and the tabs seem to flex, which keeps them from putting enough pressure on the gaskets…
Just to clarify, my DrDiff master has been on a couple years now. Noticed very small seepage from the forward cap after driving Friday. Just picked up the 42044 and 42081. Surprisingly to me, stronger material caps, thicker gaskets, snugger fit. I’m sold.