The rear transmission mount (or engine mount) is located under the car on the transmission (driver's left) side. This is a rubber mount held between 2 metal brackets.
When to replace
I removed the wheel for visibility and ease of access. Before raising the car, loosen the lug nuts (but don't remove them).
Raise the driver's left side of the car. Use a jack stand, positioned at the jack point. Rock the car to check that the jack stand is positioned safely.
Remove the wheel completely.
Underneath the car, apply WD40 to the all nuts holding in the mount, but do not remove them yet.
There are 3 nuts facing downwards on a triangular wedge shaped metal brace attached to the chassis of the car - 2 of these nuts are bolted to the chassis, the third, closest to the front of the car, is attached to the rubber mount its self.
On the forward side of the rubber mount here are another 3 nuts attaching another metal brace to the transmission housing. These bolts are facing horiztonally towards the the centre of the car.
You will need to use the car jack to support the transmission whilst the old mount is being removed.
Place a piece of wood on top of the jack to provide some cushioning and a larger surface area so that the transmission housing isn't damaged. It shouldn't get damaged easily, but it's a good idea to protect it a little.
Slide the jack in from the front of the car and raise it slowly so that it's firm against the transmission housing.
Now that the WD40 has had time to do its work, undo the bolts holding the 2 brackets in place. These are all 17mm.
I removed the 3 downward facing chassis bolts first, including the one attached to the rubber mount, keeping an eye on the engine for any movement.
The triangular wedge shaped chassis mount comes away in 1 piece, seperated from the mount.
Once the chassis bracket has been removed it's much easier to undo the transmission nuts and remove the 2nd bracket and mount together.
With the 2 brackets and mount removed from the car you can seperate rubber mount from the bracket more easily.
There are 2 14mm nuts on one side, 1 17mm nut on the other.
With the old mount removed you can reverse the above process with the new mount, attaching it to the transmission-side bracket.
I used Loctite Blue on the nuts.
Attach the transmission bracket first, then the chassis bracket. The chassis bracket allows for some positioning before being secured. Note that the middle nut's inner diameter is slightly smaller than the others (though all nuts are 17mm).
Again, I used some Locitte Blue.
Once done, remove the jack and replace the wheel ensuring to only slightly tighten the lug nuts.
Once the car is back on the ground tighten the lug nuts completly.
Test drive, listen for any clunking noises and look for any engine movement when idling.