Antares 760 Nanni engine mounting bolts

I own a Beneteau Antares 760 with a Nanni 200 HP four cylinder engine. I have had very serious problems with the engine mounting bolts of which three out of four have sheared twice, once in 2009 and again in 2018. On the second occasion the stern tube was also damaged. The engine only had 1000 hours on the clock by 2018. If the engine had broken loose before the problems were discovered on each occasion the consequences could have been very serious. Has any other sister ship owner had a similar experience?
Peter CARDEN