We almost never replace modulators. I suppose they could stick and I have actually seen them leak both externally and through the diaphram, but the common issue is just a matter of adjustment.

I hate the modified one with the plastic cap. The adjustment range is about useless and the cap is pretty much destroyed when pried off. The old rubber reusable cap worked just fine and was probably just too easy. I'm relatively sure that is why they changed it, because too many folk were making ill considered adjustments.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician