Front And Rear Differential Vent

[NeVeRsUmMeR]

I have a question on the vent for the front and rear differential.

 

1.) Front Differential takes either 75-90, 80-90 Gear oil, but if I switch to Synthetic what do I need to do with the vent? Also will 2 quarts fill it?

 

2.) Rear Differential takes 75-90, is this synthetic from the factory?, or not?? Also I want to run synthetic do I have to do anything with the vent?

 

I've read that if you change from gear oil to synthetic gear oil you have to change the vents, so i'm wondering what color for the front and the rear vent is currently and what they need to be to run synthetic, and if it is necessary?

 

The truck is a 2002 half ton 4X4

 

I appreciate the help from everyone.