HONESTLY I would think more on poor positive contact around. we can talk about bulkhead, ammeter stud, Battery terminal, alternator stud, starter relay stud.

another positive point to check is on back of fuse box... buss bars. Terminals get sulfated/corroed. ACTUALLY I'm working on a Dart fusebox with that problem, where quite often loose the cluster lights, wrong gauge readings, and even non working back up lamps! We discover is on fusebox. FUSE TERMINALS WERE GETTING INCREDIBLE HOT and then cluster lights died. Fuses never blow. We are using battery ends cleaner since that is used to remove sulfated surfaces

clusters normally does have LOOOOOOTS of ground locations with each screw what makes me hard to think a ground problem. I never have found a ground problem on a cluster... maybe yes on block, ground body strip or something like that

AND REMEMBER it couldn't be a ground on cluster if we are talking about gauges BECAUSE GUAGES ARE DRIVEN BY VARIABLE NEGATIVE coming from senders, so gauges are isolated on cluster