That 36 X was made in 1985 .
Every Leupold scope produced since 1974 will have a letter included in the serial number acting as a date-code. Scopes using a letter as a prefix (the beginning of the serial number) were produced between 1974 and 1992. Scopes using a letter as a suffix (the end of the serial number) have been produced after 1992. On the chart below, you will notice the letters “I,” “O,” and “Q” have been omitted as they are easily mistaken for “1,” “0,” and “0” respectively.
Prefix Suffix
E = 1974 A = 1993
F = 1975 B = 1994
G = 1976 C = 1995
H = 1977 D = 1996
J = 1978 E = 1997
K = 1979 F = 1998
L = 1980 G = 1999
M = 1981 H = 2000
N = 1982 J = 2001
P = 1983 K = 2002
R = 1984 L = 2003
S = 1985 M = 2004
T = 1986 N = 2005
U = 1987 P = 2006
V = 1988 R = 2007
W = 1989
X = 1990
Y = 1991
Z = 1992
Glenn