I have a pair of the Mt. Experts also.
When I first bought them about 3 years ago, Lowa recommended using Granger's products that are safe with Goretex. It was Granger's G-Max line. I see Lowa has since changed their website, and Granger's has changed their products also.
Back when I bought the Granger's stuff, they had several different products for the different kinds of leather. Now, they have two products that I see: G-Max Universal Footwear Waterproofer, and G-Max Footwear Waterproofer. I don't know the difference between the two.http://www.grangers.co.uk/US/productview.cfm?id=33http://www.grangers.co.uk/US/productview.cfm?id=31
I think it is kind of odd how Lowa doesn't mention anything about Goretex vs. Non-Gortex boots. Maybe give them a call or email to inquire about the proper treatment of the Mt. Experts?
Also, even after using the Granger's products (the old line of products), the water does not bead up on my boots like I expected it too after the treatment. It kind of sucks when the leather soaks up all the water. I might be looking into a new solution. Keep us updated.