Digital Odometer / Gear indicator lights flicker

The digital odometer and digital shift indicator below the speedometer and tach in my '98 Blazer 4 x 4 flicker. The problem has gotten worse and started staying off almost all the time. If I knock on the plexiglass over the guage cluster sometimes they will pop back on. This being the case I though it was probably just a bad connection, but I took the guage cluster out and the one wiring harness hookup seemed to be good an tight. Everything else on the cluster works normally. I then bought a new to me (used) gauge cluster off of ebay from another '98 and after installation things looked good. The lights stayed on consistenetly for a couple weeks, but I am now back to where I started and they are flickering and staying off again!!! PLEASE HELP, I need to record mileage for work and with no odometer it is quite hard..... :banghead: