Here is the response from LeatherTech.

Dear Stu,

I am so sorry to be the bearer of bad news but,
The type of soiling you have on the type of leather your holster is made of can not be cleaned out, any attempt would be futile.
If you would like to purchase a protectant to apply to your next holster to increase its ability to resist this type of soiling,
I have attached a link for the best product I have found in 21 years of cleaning and protecting leather.
http://leatherworldtech.com/Products...__LMPC250.aspx