About a month ago I drained and replaced the front and rear differentials with Mobil 1 75w-90.

Now I read that the vent plug needs to be replaced because it "rots" with synthetic fluid in the front differential.

The questions are:

1. Do I have to replace this vent plug with the correct one immediately, or can it wait a few (2-6) weeks?

2. Could it do permanent damage? Or does it just start to leak?

Thanks in advance

#2 first - it's my understanding that it just leaks
As far as #1, I changed my front diff to synthetic three years and 100,000 miles ago on the "wrong" vent plug. Still there, still holding, I'm not losing any sleep - I think you're safe for a little while!

Is it a o-ring seal?
I work on turbine engines that use synthetic oil.
I also work on diesel engines ronning 30 wt. dino oil.
Same O rings.

As far as #1, I changed my front diff to synthetic three years and 100,000 miles ago on the "wrong" vent plug. Still there, still holding, I'm not losing any sleep - I think you're safe for a little while!

Same here.... on the GMC

As I understand it, the difference between the white and black vent plugs is not the o-ring but an internal baffle plate. The body of the plugs and the seal ring are not synthetic incompatible, but the synthetic's lower flow reisistance would cause "pumping" up the vent hose when being splashed by the gears in the diff. I meant to do it shortly after reading about the "necessity" for the change, but kinda put it off and pretty much have decided that it's not necessary for me.

As I understand it, the difference between the white and black vent plugs is not the o-ring but an internal baffle plate. The body of the plugs and the seal ring are not synthetic incompatible, but the synthetic's lower flow reisistance would cause "pumping" up the vent hose when being splashed by the gears in the diff. I meant to do it shortly after reading about the "necessity" for the change, but kinda put it off and pretty much have decided that it's not necessary for me.

Now that actually makes sense. If it was something else, like synthetics "eating" o-rings, synthetics would have caused a ton of trouble by now with millions of cars, and not just with differentials. Oil filter gaskets would have been leaking like swiss cheese the world over.

Thanks. I can now sleep better and I feel smarter too (but I am still going to switch that thing out next time I have reason to get under the truck)

I agree with Idle_chatter. I believe the difference is in the internal baffle. On the white ( synthetic friendly) one, the baffle is metal instead of plastic. Therefore heavier. This seems to make it stay pointing down better.

Tom, I never put much faith in the reason GM published. I decided to run mine with Mobil 1 and watch it. Being an Engineer I am sure you have head that before. It has held for 61K so far. Later! Frank