Mike:

YES! Replace the head bolts .... they're only like $1.50 each and the reason you have to replace them is they stretch the first time they're torqued. You won't achieve the same torque again, and might strip the threads if you try to retorque them again.

The 90 degree rotation is done after you torque to the required 70nm. After torquing to 70, follow the torquing diagram sequence and turn bolts 90 degrees. Then return to #1 AGAIN and turn 90 degrees again going in sequence. The head is then secure.

Good luck!

~Paul

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'91 300E, 206k miles