The film This is Spinal Tap came out in 1984. It was made for a very low budget, was a huge success, and has since lived on via home video, cable, CDs and almost every form of exploitation you can imagine. Its creators — Christopher Guest, Michael McKean, Rob Reiner and Harry Shearer — were entitled to profit participation of 40% of net receipts based on all sources of revenue including merchandise and music. Guess how much they've received in those payments in the 32 years since that film first hit theaters. Guess real low.
Harry Shearer has filed a lawsuit which may well be worth watching. Folks who feel ripped-off in such situations usually threaten, sometime file but almost always settle for five or ten cents on the dollar to go away. I know enough about Harry to know he ain't gonna do that.