The thread area stretches/deforms on "torque to yield" fasteners. As the "yield" in the name implies, the tensile strength of the bolt materal is exceeded with the "+90 deg" 2nd stage of tightening.

Stiffener plate bolts MUST BE REPLACED after each removal. A set runs around $25.

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'03 X5 4.4 Sport, last of the M62s (8-03 build date)
I believe in deadication to craftmanship in a world of mediocrity!