Post Season 3 Location?
My wife and I have loved this series since the late '70s and it has to be among our top five all time of anything.
That said, we noticed on the Season 4 DVDs that it states at the end credits, "A BBC production.....and the Australian Broadcasting Company". Were these later episodes (1988) still filmed in Yorkshire or was some of it done in Australia.
Also, I wouldn't mind getting involved a little with a friendly forum about ACGAS. If you appreciate the series, you're probably "good people".