A machine goes down at 2 a.m. Maintenance identifies the failed part within twenty minutes. Then the real problem starts: the OEM quotes a six-week lead time, the internal stock room doesn't carry it, and nobody is sure whether the aftermarket unit sitting in a supplier's catalog is actually interchangeable. At that point, the bottleneck isn't mechanical anymore. It's procurement. This is why the choice of MRO supplier matters far more than most purchasing scorecards suggest.