OK, so it's fixed! FOR GOOD! I had the propshaft removed on my 2010 Brera Q4 and had the bearing fixed.
As per the experience of others on the forum, i was unable to find a driveshaft specialist that could just replace the bearing (despite going to 3 different workshops).
I am in Perth Western Australia and gave it to my father in law who is a mechanic to remove the propshaft and take it into "his guy" to get him to do the repair. Apparently he said it's some sort of special light weight piece of kit and recommended taking it to Hardie Spicer who actually manufacture driveshaft components.
So... he did that, and the Hardie Spicer guys concurred and said that there is no workshop in Perth that can re-manufacture this part, however, they have a sister company in Germany that specialises in these customisations.
So, after a few weeks (about a month) the part was air freighted across the world, re-manufactured into what it SHOULD have been in the first place, which is a driveshaft that uses commonly available REPLACEABLE bearings and CAN BE DISASSEMBLED, and popped back on...
...and it's SMOOTH as a baby's bottom. No knocking on take off, no vibrations....
Whilst the part cost me the same as what the original OEM part would, it is now PROPERLY made and the next owner will be able to change the bearing for a couple of hundred dollars instead of $3000...
You know, i still can't believe that the Torsen guys actually think that the original non-replaceable design is acceptable.
Here's a video and some pictures of the undercarriage of the Brera with the exhaust system for anyone that needs it for reference.