We went to HWH Europe premises in Oldenzaal. After cleaning the jack several times and extending and retracting they discovered the fluid line connector was leaking. After tightening the connector and extending and contracting a few times just to check, the leak was solved. They also checked the reservoir fluid and topped it back up with a litre of hydraulic fluid.
Hopefully everything is now OK.
As we left the guys at HWH asked if they could take a photo of the coach outside their premises. We kindly obliged. Thank goodness the coach was looking fairly clean!