G18 at 123W is sandwiched between the stronger signals from 119W and 125W.
For me, G18's signal is hard to pick out with a analog beeper type meter (which is the only kind I have). When listening with the beeper, it is hard to pick out G18's weaker signal between its noisy neighbors.
Set up your receiver and a small TV right by your dish. First find 119W, which has a very strong signal, then mark the position of your mounting pole to dish mount rotating/clamping collar with a pencil. Go to the antenna setup/installation screen for your receiver. Set your receiver to a strong transponder on G18. You may need to manually enter the values. (There is good info on strong transponders for each FTA satellite on this site.) Slowly rotate your dish about 1 mm at your pencil mark to the West. You should now be very close to 123w G18, and hopefully you will see some signal quality on your chosen transponder. Peak signal and enjoy! If you go too far and get 125W, make another pencil mark, and know that 123W has to be right there between your marks.
Hope this helps, I spent many frustrating hours trying to find G10 then G18 before figuring out the above after much online study and trial and error. Now I can find G18 in a few minutes with a 30" or larger dish.