Friend who was in the Toyota Owners Club in Sydney for many years did many tests on fuel consumption in large 4WDs with freewheel and locked wheels when used on the bitumen (so in 2WD) and he reckoned there was not enough difference to be worth the hassles of getting out into a mud bog to lock the hubs. Wheels spend 99% of the time in the straight ahead position so diff and front drive shaft aren't working so how much energy is needed to spin the front axle.
Another friend with an OKA replaced his locking hubs with fixed hubs for the same reason and has never regretted it.
Once I get out where there are gravel roads, I lock the hubs and mostly drive in 4H to improve stability on loose surfaces.

On the other side of the equation - well, actually still arguing for locked hubs - are a couple of friends who have spent a considerable time searching back over a sandy track looking for all the bits and pieces that erupted when the locking mechanism let go


As for front diffs leaking out the axle seals, if you have dana axles then in some builds the front one is upside down which means the fill plug is about 2" higher than the back one so there is more oil pressure wanting to leak out. Leave the oil level way below the fill plug and there will be way less leakage.

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Tony
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