Thank you for your kind replies. sl_status table in the slony schema
shows st_last_event and st_last_received are growing.

No errors in the Slony or Postgres log files on the master nor the slave.

I've shut down the slave and master; dropped the DB on the slave; and
recreated the replication set.  It's copying across now (23 GB).
We'll see how it holds up after the resync.

Thanks!
Aleksey