Gday Ruks.... :)
Nice pick-up mate, great grinder the Cadet. 8-)
Regarding the damage to the burr carrier thread, you should be able to obtain a Thread-Chaser tool that can be used to remove any indentations, etc. Conversely, you could also a very fine triangular file for the upper burr carrier but if the static thread in the main casing is also damaged, you will definitely need to use the chasing tool mentioned above.
These usually can be obtained from a decent tool store. Just take the Upper Burr Carrier with you so that they can measure the thread and supply you with the appropriate tool.
Re: seasoning the burrs... I dont think you need to do anything other that grind some fresh coffee through the machine and all will be well. You dont want anything other than coffee inside there.... ;)
All the best,