Historically (I believe) Letterboxes were found by following clues, and obscure directions, like a treasure hunt (~1854, Dartmoor, England); with the suggestion in 1907 of the Finder using a homemade inked stamp to stamp the Letterbox's logbook, and using the stamp of the Letterbox to stamp their own log book (or postcards left in the letterbox container) to identify that they had actually been there. The Letterbox Hybrid is similar, but a GPSr is generally required to find the cache. There is not the obligation to have your own stamp, but if you do, could you please stamp the log book.
It is quite a dusty drive out along Mooral Creek Road from the Comboyne Road, (which goes from Wingham to Killabakh, and up to Comboyne) - and a lot of car GPSr’s will want to come in by Warrawillah, which does work, but not the quickest or most direct route. Now (August 2015) the bridge just north of Wingham (Potts Bridge) is open again. If you choose to go onto Warrawillah Road off Bulga Road @ S31º 45.935' E152º 18.915' try not to pick a time when a school bus would be on the road, as often it is ONE LANE.
So, how do you find this elusive Letterbox in this delightful rural location ?!?
You may be able to work out some of this before you hit the dirt road, and possibly out of 3G reception.
Head to S31.720238º E152.355657º, where, if you have found a 'certain' "Souvenirs Challenge" geocache you will be at an advantage (especially if you click on the fourth possibility of the "Find..." section below that cache page) for looking for a 6-digit number, on a permanent steel plate, 10 cm x 2 cm.
I will call it "ABCDEF".
The 'rural address' of the community organisation west of the Community Hall is "GHIJ", and is on a metal plate 35 cm x 13 cm.
While nearby is another metal plate, 15 cm x 7.5 cm, the upper number being "KL", on an utility item close by, and the lower number on that plate is "MNOPQR"
Then go to: S31º 4(A+G).JKB' E152º 2C.HQM'
Please park responsibly, and replace the cover as found. (This was the place offered me by Paul, if you are wondering). You really shouldn't need the Additional Hint.