Wolo Dixie air horn problems?

I bought a Wolo Dixie air horn back in 2003. I used it back then in a truck I had at the time but took the horn out when I got rid of the truck the following year. I kept the horn all these years and just recently installed it in another truck I just bought. I noticed the on one of the trumpets that the back part (the black piece) was loose. When I play the horn, it misses a few notes in the middle even though everything is hooked up. I oiled the compressor and tested it and all the air holes blow air. Does the loose back on that trumpet have anything to do with the notes being missed or is there something else I should check? Thanks in advance for any help you can provide!!