Some people wrongly believe that servicing a trombone slide means just "taking the dents out". There are actually many things that need to be right in order for it to be a really excellent slide:
1. The slide must be free of dents, of course.
2. Both inner and both outer tubes must be straight and round.
3. The outer tubes must be parallel in all planes.
4. The inner tubes must be parallel and the correct distance apart.
5. The inside of the outer tubes and the outside of the inner tubes must be smooth and polished.
What my slide service includes:
1. Check and straighten inner and outer tubes.
2. Check and adjust, if necessary, alignment to 1/1000 inch for both outer and inner slides.
3. If needed, chem clean outer slide.
4. Polish inside of outer slide.
5. Adjust waterkey and replace cork if needed to ensure airtight seal.