MZ/MuZ Riders

Now that I've finally got my ES125/1 working (after chasing a dead ignition coil for weeks that worked out the engine but not under compression (even though it should have been my first guess after dropping the original down the stairs )), I'm moving on to the odd jobs left on my bike and one of those is figuring out how the toolbox cover stays on.

It currently has a bodge of a universal key lock (without the key) that isn't a very good bodge because it doesn't actually hold the cover on at all. I can get hold of the correct size lock easily on eBay, however looking at the drawings for it in my manual I come across something else I'm missing called a 'lock plate for safety lock' (13-28.090 item 8, picture below)

https://photos.app.goo.gl/TvwVDRhFFABnH8pM6

Can anyone please explain what this is actually for? A brief search online reveals nothing, so if I need it for the cover to stay on, does anyone know of anywhere (ideally in the UK) where one could be sourced?

Also, there appears to be some sort of gasket (item 4 on the picture) which I assume is used to seal the toolbox cover against the fairing, can anybody confirm please?

Thanks

i think it locks the key lock in the outer cover maybe by being turned 1/4 turn after being installed
on the lock on back side of tool box lid
my German - = 0 and the German to English translate programs are not much better some times

compare that o ring to the air filter or air filter lid / cover