you can just get a new motor mount from the junk yard for hopefully around $30-$40 or maybe cheaper...you don't have to pull the engine out if you're just replacing that one motor mount since you still have 2 remaining mounts left hooked up. to be on the safe side you put a jack under the block to get additional support, plus it makes it easier to remove the mount. mine is the same way right now, i found that out when i was going to install motor mount inserts. i didn't have time so i just put the inserts anyway and i'll just get a new mount when i get a chance. it's ok so far...i took it to the track last week and i did fine. the car doesn't shake anymore when i'm rolling from a stop...but the vibrations are there, not because of the mount being busted but because of the inserts.
the inserts take the play off from the motor mounts so even if the mount has a crack on rubber part of it, you should do fine. though i recommend that it's better to get a new mount, and if you have the inserts already, you'll do all the hard work in just one time. hope this helps!
