Don't know why it's called "gear box cover" but it's the cover behind the alt. belt cover, p/n 11147713872 (orig. p/n = 11147675924).
Drawing # 11_3592 it is part number 1.
Significant corrosion on the lower portion of the cover but the worst part is it has resulted in 2 of the lower belt cover bolts (#8's - M5 x 16) lost their heads and part of the shafts when I tried to take the belt cover off. 1 bolt, the very bottom, still has a bit exposed so I may be able to get the remaining part of the bolt out. The other bolt will require drilling and easy out to get that bolt out. The issue is the cover metal is definitely corroded, I would just like to replace it if it's not too
I have applied several squirts of PB Blaster to the remaining portion of the bolt and will let it soak overnight but with the corrosion in the metal don't know if it will let loose.
So, how much trouble is it to just replace the metal cover? It's an expensive part ($280) so I'm not thrilled about it but.....
I would suggest everybody pull out the bolts securing the alt belt cover and apply a liberal amount of anti-seize on the threads even if you're no where close to replacing the belt to make them easier to remove when you do need to replace it.