Not copper grease my mate and only if its silicon grease not sealer! 🤔, you don't have any other grease to wet the oring outer surface which will allow them to slide in while fitted on the pipe end?
I simply swapped the radio for a modern unit, gaining the microphone for calls as well and then traded the old unit for some bits.
There is a mod on the YouTube that is a little more involved than I wanted to be. 👍