Diff breathers are raised because it's easy to do and cheap
insurance against water getting into the diff.
Your 90 series Prado will have the front diff breather raised
to the level of the chassis. The rear breather sits on the axle
housing. They both have a one way valve which stops water entering
thru the valve, but the problem is that when a hot diff hits the
water, then air inside the housing cools rapidly and contracts,
the valve closes and water can then get sucked in past the seals.
Out of interest, you often hear the suction when you undo the nut
to check the oil level in the diff.
To raise the front breather , you need to remove the valve, fit
a 1/4 inch male/male barbed fitting, then about 18 inches of 1/4
inch fuel hose and pop a cheap fuel filter (say Ryco Z92) on the
end. Use cable ties to secure the fuel filter high in the engine
bay. Job done.
For the rear, you need to unscrew the valve (14mm ring), fit a
1/8th BSP - 1/4inch barbed brass fitting, then about 1.2 metres of
1/4 inch fuel hose. Feed the hose up out of the way towards the
compartment where the jack is stored. Make sure the hose is well
secured to the barb fitting and that there is enough slack to
allow for suspension movement. Slice a hole just off centre of the
grommet which takes the wiring into the jack compartment. Feed the
hose thru - might need to wet it to make it slip easily.
Sometimes this is easier if you pull the grommet out first.
Find it from the inside and pull it thru. Seal the slit in the
grommet with a smear of Silastic. Attach a fuel filter to the end
and secure it with cable ties high in the jack compartment.
Cheap and easy to do, so just do it!
NOTE: The gearbox and transfer case breathers are a tad more
difficult to access and are not covered in this report.