There is this clear manifold that is cracked and broken. I am not sure what it is. Its not the main manifold, its something else. There are also a bunch of hoses that look like they should go to it, BUT they are not connected. Any ideas what this is? BTW, this is a 1995 Hurricane/Pinnacle Hot tub.

Here is a pic

Looks to be your air manifold. your jets tie into this for their air venturi induction that produces the bubbles at the jets. In my opinion, unless you have water back feeding through this system and leaking out that manifold, I would just leave it as is. The only thing it will do with cracks is maybe still have some air at your jets when you turn the jet air control knobs all the way closed. You can replace it with any standard air manifold. Many companies sell these.