You are lucky the errant nut did no damage. I would consider adding good fuel filter. Glad to hear it's up and running.*
The nut falling off caused a little nick at the very end of the valve. Nothing a little emery paper could not remove.
It does have an in line fuel filter. One tech I spoke to in the US recommended it be for 50 micron. However, everyone sells a generic in line filter for diesels without knowing that specification.