Thanks for the clues, Mark. Mine has a cast body with a felt sleeve over the top, the felt is retained by a washer which is held on by the tygon tube attached to the clunk. The holes through the clunk are quite large & the feed rate is very modest, the Wren 44 runs about 8 minutes on 50 oz Dubro tank.

The clunk has only recently returned to service after being dry for months. Do they take a while to get thoroughly wet through? - John.