How long should they last? I would say 178 K miles or less. They are not difficult to change. Take extra care to make sure that the engine doesn't move after you lift it to get at the broken mounts. Very important because you WILL get your hands into dangerous locations. Use a good quality allen head socket wrench with a ball head to get at the bolts from underneath. You may need to pry the engine fore/aft or port/starboard to get the proper bolt allignment in the access holes.

Do the engine mounts for now if they are broken and have a look at the trans mount. It will likely be OK...they last somewhat longer.

Take care and be safe!