I've been thinking there was a bit of diesel smell for a few days so had a look. When I touched one of the leak off pipes it hissed ...
changed them all yesterday. How many came off without breaking? two. All the others broke off at the wee nozzle. Perished. It was like surgery trying to get all the bits out. Had to raid the fishing bag and get the forceps...
Questions:
Does the braid on the outside serve any purpose? or is it just there to rot and make a mess?
Is it possible that it could be running a bit smoother after changing them? I can't see how it would affect it but could it have been drawing air through the broken pipe? but I thought this just went back to the tank ...

Leak off is exactly what it is, the amount of pressure to the injectors isn't all used and some leaks off via those hoses and then down to the pump return union to the tank using a venturi effect it draws the diesel away. The fabric was devised to allow them to rub against other things without wearing a hole in the tube. Pearl do a leak off kit with all the stop ends in it, Local motor factors keep it on the shelf.

Get good ones, the ebay ones are crap, and crack go brittle