Fuse box problems on 1977 and 1978 Mopars

On my 1977 and 1978 Chrysler vehicles, I keep getting this problem where my instrument lights and tail lights die. Upon troubleshooting, I find power at one side of the fuse in each circuit, but not on the other side, and it is not caused by a blown fuse. The fuse holder is intermittent or gets too dirty easily, or something. I've replaced the fuses and cleaned up the fuse holder twice now. After I clean the fuse holder, both circuits will start working again, but then it happens again a few months later. Maybe I haven't discovered the actual failure mode. What else can I try, or what should I do to fix this problem permanently? Should I replace the fuse holder? Any suggestions on a high-quality fuse holder that I could use to replace the original Chrysler item?

Thanks a lot.