Clutch Master Cylinder Failures

Experiencing several clutch master cylinder failures (cracking occuring adjacent to fillet strengthening the boss accepting hydraulic line) following replacement of dual mass flywheel with Heath single piece flywheel kit flywheel, friction and pressure plate). Also replaced pilot bearing, fork, pivot assembly, throwout bearing and slave cylinder at same time. Replaced hydraulic line after first master cylinder travel (line only support at right hand upper bellhousing bolt). Last couple inches clutch pedal travel (both application and release travel) stiff. Have used GM and other brands master cylinder, all have same markings so appear made by same manufacturer.
Other related threads read but don't seem to offer answers.


Did get a reply from a5150nut on 6.5 forum but am open to any other ideas!