Just a random set of dates for you to play around with.
A = 25/04/1954
B = 23/05/1959
C = 18/06/1964
D = 03/07/1978
E = 03/01/1979
F = 09/02/1980
G = 16/09/1984
H = 09/03/1987
J = 01/01/2004
K = 17/08/2011
You need to find a single digit for A to K and then you will be able to find the cache at:
N51 24.(H+D-C) (J+G) (K+J)
E000 23.(E/D) (A-(B+G)) (G-F)
Happy hunting.
Congrats to GeoCotch on the First to Find, it's just a shame that the First to Solve has not been able to get out to it.