1969 318 in a coronet leaking oil from the plug. Tried a self tapper and the self tapping threads got eaten while inserting the self tapping plug. Purchased a helicoil kit from NAPA (1/2 x 20) for $48. Drilling out the hole (33/64 bit and another $20) seemed fairly tough but was accomplished. Tried to tap the hole and the threads on the tap got eaten. What is this reinforcement around the drain hole made of ? Need a top of the line tap ? Is there a trick to this ?
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