I've worked on a few 68-70 B-body clusters and I will say in my opinion, they're a piss-poor design at best. They're right up there with the '67-'71 Dart's with a two-peice board.

What you might want to do to avoid more problems is if you have the cluster out, take it apart. Pull the gauges right out and clean the threads on the studs on the back. Take some steel wool to them and get them spotless. Do the same to the copper "pads" on the circuit board. Be gentle on them though - just make the copper nice and shiny.

Lastly, upon reassembly, use some dielectric grease on, around and between the nuts that hold the gauges to the board. The grease will prevent further oxidizing and help preserve all the various metals on the cluster.

It also never hurts to add a secondary or tertiary ground wire. You can never have enough grounds.