2017 CX-5 Rear differential oil leaking

[moonj]

I have replaced the rear differential oil 1 year ago, and today just noticed some leaking on the floor.
It was fine during the year, not sure why it's leaking now.

I used the old washer as I forgot buy one last year. What you guys think on this? Should I just change it again? Not sure which part is leaking yet.

 

[moonj]

Anyone knows the part number for the crush washer?
I double checked it, might be the top hole and looks like a little bit loose. (I only used a 23mm wrench to tight it last time. Will see if it will leak again--Is there a required torque on it?)
I am thinking just open the top hole and add some oil in (since I still have almost 1 bottle) and use a new crush washer on it.

 

[moonj]

I just used some brake cleaner to clean that and will monitor it for a few days.

Also is this part normal in picture? Not sure if here will cause any leaking? (Up is front----Down is rear for the car) I still think might be the "FILLER Plug"
Mazda CX-5 Service & Repair Manual - Differential Oil Replacement - Differentials