1974 GMC Envoy

I have a 1974 GMC pickup with a turbo 400 transmission 80000 miles since a rebuild. Pulling the pan for filter/fluid change I found two small pieces of metal as if from small washer. A transmission shop thought is was from a pressure seal. The transmission has been slow to shift into reverse for several years but other wise works very well. Is it possible the transmission will continue to work as is for a long while or short term failure? I drive the Pickup about 2000 miles a year for camping/fishing. Thank You in advance for your expertise.