I had one break while tightening it after I had replaced the mounts. Oh ... dear ... motor mount bolt busticated It was kind of a puzzle to remove the stranded piece of bolt. After that I replaced both ... got them from the dealer and they weren't outrageously expensive.

While mine did break, I don't think one is likely to break on its own, although I'm not an expert in physics. My bolt broke under extreme torsional force (I idiotically WAY overtorqued it) ... that type of force wouldn't be reproduced by the engine or movement of the car.

The correct torque is 75nm. Don't go over that ... read my thread.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)