A letter and single digit number are the year and quarter.
The letter is the year starting in 1931.
The number is the quarter (4 quarters in a year).
(example: "E4" is the 4th quarter of 1935)
A = 1931
B = 1932
C = 1933
D = 1934
E = 1935
F = 1936
G = 1937
H = 1938
I = 1939
J = 1940
K = 1941
L = 1942
M = 1943
N = 1944
O = 1945
P = 1946
Q = 1947
R = 1948
S = 1949
T= 1950
so I have 2 sturmeys that i've recently acquired from some 50's era western flyers. I'm guessing they need to be cleaned to work as they once did. it looks like i need some tool from the diagram. are these hard to find, or can i use something else that wont ruin them?