I’ve bodged a temporary fix from an Aldi plumbing o ring and seal set of all things.
Luckily there is a rubber seal in that kit that just stretches onto the available shelf of the upper seal. It sticks out a bit, but that’s probably a good thing to stop stuff dropping in. There is still a smaller gap to the top of the compression ring, but I’ve wadded a load of grease into that, so unless I ride it in a monsoon, it should keep dust etc out until I can take it back to the buffoons. I will only be riding a couple of times until I can definitely get it back to them, so should be fine until then.
As suggested, I will print off the documents and try to get all the bits back and do the damned thing myself. All I really needed them to do was press the bloody cups in!
I won’t go in all guns blazing as that is obviously not a nice thing to do, and could prove counter productive. If they mess me about or won’t give me the bits back, then a public flaming may be in order. Having said that, I’ve always found them alright on a personal level, so I think this is incompetence rather than malicious.