After some web searching I found that the most recommended substance to glue polycarb is Weld-On#4. It's a solvent adhesive. They do not recommend using any kind of "super-glue" ever, as most are made from cyanoacrylate which will damage the polycarb. Solvent adhesives are the way to go. They are not really cheap though. There's a site called eplastics.com that sells a 4oz can for around $6.30. Sounds like a lot but the substance is water thin, so not much is needed at one time.
Hope that helps
