2003 Mazda MX5 Speedometer Issue

Hello, My speedometer occasionally stops working. It will drop to zero while I'm driving & stay there for a matter of seconds or even minutes. Sometimes it jumps from working to not working several times before working again. My dealer says they'll need to replicate the situation in order to check it, but generally, it works about 95% of the time. I'd like to get it fixed before it gets worse.