Cars running fine, however when I start it up or turn it off there's a pretty significant shutter/thump felt. I know a lot of you have upgraded the rear mount. Is it a common failure? I have 52'000 kilometers.
I agree with the maybe.
The stock lower rear motor mount is pretty flimsy. If the rubber part failed it would be giving you thumps like you describe.
It is rather easy to check. Pull off the under engine shield, look at the back of bottom engine, wiggle it. (with pushing leveraging with a longscrewdriver or other tool) If the engine rocks back and forth.. moves easy your mount is shot.
I suggest buying the ERMM for $45 or so (US..)
When the mount fails, the engine can move about two inches rocking at the bottom, and it will bang into the firewall.