I've broken plenty of allen keys inside of pins before, but typically whilst removing them. It sounds like you may have the wrong pairing of collar and pin.
More information needed...
Type of fluid, seals, filtration.
Contamination level of subject unit and upper acceptance level for the same.
Area of leak.
Condition of the "chromed" component (agree with poster above that hard chrome is applicable in almost every instance).
Pictures?
