240 Motor mount breaking again and again

I am having a problem that I can't figure out. I hope someone knows what the problem is.

I have a 74 240D. About 6 months ago I was rear-ended (mild damage). About two days later the left motor mount broke. When the mount is broken, there is strong engine vibration.

I replaced the mount and everything seems fine.

The motor mount broke again in a few weeks driving. It has broken again and I have replaced it again two more times.

Does anyone have an idea what is causing this?

I tried loosening the fuel injector tube on each cylinder while it was running and found that each cylinder has the same effect.