Visual inspection methods for case head failure

Anyone found a good way to do visual inspections inside the case for head separations. I know about using a sharpened paper clip etc for investigating them. I guess I was looking for a cheap rigid borescope or similiar idea. Any thoughts

By using a bright light source(like the sun) and holding the case to see the inside case wall while rotating the case, one may see the ring(partial or full). Best-o-Luck