Hey @ConfusedAnt, from this post I seem to remember the access_type=offline query parameter was not part of your OAuth 2 credentials.
This would lead to the Google API not issuing a refresh token used by n8n to renew the actual access token (this is described for example here in their docs). So you could try simply adding access_type=offline in the Auth URI Query Parameters of your OAuth credentials and then reconnecting as described here for example.