The Wimmera was once a fairly isolated place, and some would argue that it still is. However with the automobile all of a sudden distances seemed to decrease. However, a legacy of the isolation is the many sites that once contained schools.
Even Grays Bridge contained a school, and the coordinates should put you in front of a plaque commemorating that fact. Before you do the multi sit back and enjoy the silence. Imagine this being occasionally broken up with the sounds of children laughing, singing and playing.
To find the cache you need the following information
The date the school opened = A-B-CDEF
The date the school closed = G-H-JKLM
The final location can be found at
S 36° 36.BCL
E 142° 54.(J+K) (G+M) M
You are looking for a small bison tube.