we now supply an alternative fuel connector kit for Ford Transit that does not require the use of the 'quick-fit' connector. It was our experience that in many cases this connector detrimentally allowed air ingress, Please see our listing
https://www.butlertechnik.com/item/Butler-Technik/Eberspacher-or-Webasto-Ford-Transit-Fuel-Tank-Connector-Kit-E0432T/6F5
This kit is generally suitable for later generation Eberspacher heaters, also Chinese and Russian Autoterm manufactured heaters