Possible MSD 6AL failure

Mine went out in my truck one day no spark at all . Had my truck carried home checked everthing determined it was my MSD box sent it back to get it checked. In the meantime I bought me a new one put it on and it fired right up. Then they sent my old one back said nothing was wrong with it. Who knows. I changed coils before I changed MSD boxes that didn't help. Its running now and ive got a extra box. I think once their gone their gone.