AFAIK, they weren't changing because of reliability. There were going through a series of general fundimental changes as they changed the engine management (EEC-IV to EEC-V), security (PATS external/internal to PCM), timer functions, etc.

All the bits that are going a bit funny use the same connector on the back of the cluster (there are 2 connector IIRC). They're actually contacts that are pushed against the flexible PCB, so it could just need removing and the connectors/contacts cleaning. I'd give that a go first.

Martin