I've always been partial to Sinclair hybrid ring duplexers. I know some that are over 50 years old and are still working as good as the day they were made. Excellent isolation, although the newer BP-BR duplexers might be better for sites that have other transmitters. I'm using a six can Phelps Dodge on my machine, but I'd swap it for a Sinclair in a heartbeat. A good duplexer won't be cheap new--I'd watch for a repeater group that is shutting down that might be off loading their gear.