82 GPZ550 Tach/VoltMeter works but slow response

After sitting in my garage 30+ years, I finally cranked it up, found that the Gauge works, but slow to respond to changes. When first start up Volt Meter slowly rises to above 12V. Then switching to Tach, it works, but RPM changes lag on gauge, slowly making its way to correct reading.

Any ideas what may be wrong and how to fix?