Motor mounts

On an Acert in a W900L, what is the normal life span for the motor mounts?

I have a drone issue that I am trying to get taken care of, I put mufflers back on and it didn't take care of it, so it is not an exhaust drone like I thought it was. I am now thinking maybe the rubber in the motor mounts has hardened and is letting the harmonics from the engine resonate thru the chassis. Is there a way to visually check the motor mounts to see if they are worn and need replacing?

 

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To me the front mounts look ok, the rear ones are questionable, not sure what they are supposed to look like. The gaps that I see on them makes me think that they need replaced, but I never paid any attention to them before, so not sure. With the rust that is coming out of them, it makes me think that there is some metal on metal contact goin on in there.

 

On the front I see the crooked bolts, now that you point it out. But on the rear, what do you see that says they are bad.

 

I just replaced those three months ago, they still look good, although the one on the drivers side is starting to squeak, a little WD-40 and it goes away for awhile.

What do you think of the motor mounts, are they toast? Could they be the source of the drone?