Thank you very much for your answers!
The hole is indeed the ventilator hole, but it hasn't got the ventilator in it.I will fix this.
As I said I already removed all 10 bolts on the rear and all 10 bolts in the front.
I did this because I want to clean the inside of the differential. All axles and everything inside are looking good, so I don't want to remove any parts inside.
Can I just clean the inside, put new oil in it, and install front and back cover with new gasket?
Thanks (again)!
