I think brown gunk is rusty vinegar that was spilled. In storage for decades and may be rusty, dusty, or musty. See photos and condition description, all are part of the description of the items. The item "Huge Lot Vintage Medical Equipment Tools Collectible over 20 pounds" is in sale since Thursday, April 30, 2020.This item is in the category "Collectibles\Science & Medicine (1930-Now)\Medicine, Dentistry\Medical Devices". The seller is "grandfathersgarage" and is located in Binghamton, New York. This item can be shipped to United States.