What would cause the front motor mounts of a 40 hp outboard to wear out? These are the mounts that attach the power head to the upper part of the lower unit not the attachment to the transom.
If you have a freshwater engine they are not difficult to replace. Sometimes the uppers go out due to years and years of having the fuel mixture leaking on them. Without seeing it I don't think anyone can give you a correct answer on why.
Not to hijack your post, but I have the same issue on the same motor. I have about 1/2" of play front to back at the top of the motor. Not sure if that's too much or not. I'll post some pics later today.