Thats rather a long time to have not backflushed your machine nk... :-?
Im sure a couple of Sydney locals will chip in soon but you should aim to do a Backflush at least weekly. Even if youre only having a single coffee per day, the coffee oil residue will be oxidising nicely inside the Group and wont be shifted with hot water alone. If left too long, it starts to take on properties similar to varnish and becomes very difficult to remove, even with the use of a reputable espresso cleaner like Cafetto for example.
Once you get some backflushing detergent, I think it would be a great idea to remove the Shower-screen so that you can get in behind it and clean any varnish like deposits from the Group with a toothbrush or similar. Once its all spic and span in the Group (and the screen), regular weekly backflush routines will keep it that way.... 8-)
All the best,