We currently ended up having 3 Knowledge repository making it difficult to upkeep the search indexes optimized and continue offering a consistent user experience.  Any suggestions on best practices or tools that sit on top of them to provide an enterprise experience? 

+1 for using a LLM as a chatbot, but with caveats.

A LLM like chatgpt will tokenise a response to generate a synthetic output, but is often prone to hallucinations. So you need to ensure that guardrails are up to limit the scope of potentially incorrect information; however it’s the future of KCS.

I’m currently testing this vendor as a cheap proof of concept. No way affiliated or endorsing, but it might be a good start for you as well before investing further: https://supportchat.link/

I’m sure you have heard this before but this is actually where AI (LLM) shines. You can hire a dev agency to build you a custom AI knowledge these days for 10-15k. You iwll be able to import all your knowledge repos and simply ask the AI your questions and it should be able to give pretty good answers.