Diff breather most likely.. It is easy as pie to swap in a factory locked rear end though so if you happen to find a smoking deal on an LS then go for it. You can always just swap out the third member and an axle with an locked SRs too. <img src="/forums/images/graemlins/cheers.gif" alt="" />

The entire locked rear end from an SR averages about $450

96 Montero LS 24V DOHC 3.0L.
98 Montero 24v SOHC 3.5L, factory rear locker, Winter/tow package.
63 Jaguar XKE 3.8L FHC
2000 Mercedes-Benz e430
07 fj cruiser