I had a problem with sludge with my Bach last year ... my valve oil was reacting with my slide grease. Some lanolin slide cremes can react with petroleum based valve oils and create a black sludge. I cleaned out my horn, as was stated above, and switched to Hetmen's valve oil and slide oil. I think any quality brand like Ultra Pure would do as well ..but my experience was with Hetmen's. Problem fixed..no sticky valves..no more sludge.