Dave H M,
Not sure what you mean about me waiting to tell the full story. Initially (and still), I was not suggesting I was questioning my mechanic's assessment. I was posting the info I did just to give a basic background to the reader. My purpose of the post was to seek input on the possible cause of the damage and whether it could be related to towing a trailer or how common the issue was.
The quality of my mechanic was/is not relevant to the story, at least in my opinion.
And, as it seems, some have experienced cracked mounts more than a single time in the past, although no one has connected it to the rigours of towing a trailer.
Marv