The idler or diff isn't in upside down.
I'm well aware of how its fitted.


It's been fine for a year, I recently discovered some friction so I reckon either the gearbox case is worn or something is rubbing inside the case but I can't see wear marks.
Even though its a year old it hasn't had much use as its hardly used all winter.
I was pleased to discover, after using tips from here, that I'd not lost any diff fluid!
Shame about the friction though.