Thanks. I just found this Thread on the reusable gaskets. I must check with the Jeep Dealer here to see if they carry one for the rear differential. Space is a bit tight back there.YES, there are reusable gaskets, "Lube Lockers" from 4wd.com
I've been using them for the past 3yrs and change my fluid about every 6mo. depending on how much wheeling I do or if the Jeep sat for a rather long time in the water.
API viscosity ratings for gear oils are not directly comparable with those for motor oil, and they are thinner than the figures suggest. For example, many modern gearboxes use a 75W90 gear oil, which is actually of equivalent viscosity to a 10W40 motor oil.
API GL-5, oils for severe conditions. They contain up to 6.5% effective antiscuffing additives. The general application of oils in this class are for hypoid gears having significant displacement of axes. They are recommended as universal oils to all other units of mechanical transmission (except gearboxes). Oils in this class, which have special approval of vehicle manufacturers, can be used in synchronized manual gearboxes only. API GL-5 oils can be used in limited slip differentials if they correspond to the requirements of specification MIL-L-2105D or ZF TE-ML-05. In this case the designation of class will be another, for example API GL-5+ or API GL-5 LS.