I have a 98 5.2L 4x4 Durango (all stock), I replaced the front diff fluid and didn't put any friction modifier in it. Does it matter on the front?

 

I would imagine so. You might want to get back in there and add some just in case.

 

I think the modifier is for the rear only and not used in the fronts.

IndyD

 

This is correct.
The friction modifier is for the clutches in the limited-slip differentials, which only came on the rear-axles. Failure to use the friction modifer can cause clutch chatter, and possibly clutch damage.
When I did my differentials, I was not clear on "only limited slip in the rear" and put the additive in both axles. Naturally, it will not cause damage to non-limited-slip axles.
The manual says that after a lubricant change on a LSD, you are supposed to do 10-12 slow figure-8 turns. This pumps the lubricant thru the clutches.
And, as IndyDurango pointed out in his earlier post, some lubricants say they have special limited-slip additive already added, I'd rather spend the $10 and be on the safe side, than not, and have a multi-hundred dollar repair bill, and be without your trusty Durango.

As for the PITA, I can imagine. I know on my Dakota, its not in the most conveniant location. I would suggest purchasing a fluid pump (such as one shown in the picture below).
When I did my differentials, I did not have one, but, when I did my friends dad's rear diff, it made the job so easy. After putting the pan back on, use the pump to add the new fluid.

[IMG]local://upfiles/948/0E4F6F80023C4D388AA0B961917DD891.jpg[/IMG]