But what would the correct weight be for a 4x2 sport? 75W-90?

Look under Tech Articles on this forum for an article called Chainging Front Diff Oil (or use this link). I followed the instructions and it was a breeze. The article is equally applicable if you are changing only your rear diff on a 4X2 model.

I changed my gear oil at 18K miles just prior to a long haul tirp. The oil I replaced was in great shape, so I probably just wasted my money. My only difficulty was dealing with a rip-off dealer, an experience I described on the other thread. Good luck.

http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?t=180

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William C Montgomery
The Truth About Cars
The Truth About Guns
'05 Sport 4X4, 3.7L - Black | Frankenlift II Premium, JBA KJ Lifted A-Arms 4.5 | Cooper Discoverer A/T3 - LT245/75R16, Load C