It's wax. Tuners are extremely sensitive and finicky animals. Therefore after assembly, each tuner goes through final adjustment and alignment. Component placement, length of leads, shape of those copper coils, all affects alignment. For that reason, after the alignment, most of the ares that can be affected are "set" in wax to hold them in place. You know how it's easy to bend caps and transistors out of the way? Well, don't do that in the tuner, lol.