The MGR Workshop Manual doesn't mention T4 in the section on brake bleeding. However, some forum members say it's the only way to purge air from the servo unit. I guess if any air has somehow gotten into the servo, then presumably so. Most brake bleeding (I'd suggest over 95%) will be done without a T4.
As to your specific problem, if the fluid level in the reservoir remains constant, after repeated full stroke pumpings, the master cylinder must be faulty. There's no other logical explanation.
TC
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