As I said its a hang over from when normal CS bolts were used. Also a CBA for costs of dropping gearbox off again to a Garage. The hardness of the bolts is irrelevent, its the tensile strength and the applied forces. Generally its a retention force not a clamping force, and certainly not a yield strain.

Release bearings use to be a carbon, so unlike a roller bearing had to be considered a consumable. Again, though now a roller bearing and hydraulic cylinder, the manufacturer will recomend replacement each time the box comes off.
CBA says compare the likelihood of failure after 'looking' at it, cost of new assembly, labour cost of dropping box off again.

If you go through the thread, there seemed to be reports that a hyrdaulic release clutch assembly didn't fit a cable operation clutch gearbox. XRT_si said his was OK.

Martin