You're going to explore an area that many people have driven past and few have ventured into...
Access suggestion: park at the "Wyndham South School" geocache (co-ords listed as parking area) and carefully walk, with caution, downhill along the road until you reach the Glenham Scenic Reserve sign. Cross the fence here and then navigate your way to the geocache. There are no trails.
You are looking for a 10 litre bucket, placed amongst a group of about six tree ferns. You'll know you are getting near when you cross the "stream" marked on topomaps. This is fringed with tree fuschia.
Winter conditions will be muddy and greasy.