Most plastics starts to soften at 350F so get it to about 500-600. If the bolt is rounded more torque will round it out more. Try pounding in the next size bit that will fit.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked