4x4 Differential -- vent or closed system

My Kubota (MX5200HST) front differential is a closed system with Kubota's Super UDT2 hydraulic/ transmission fluid in it. After working the machine and getting the fluid in the differential hot it will build up a substantial amount of pressure. If I vent the pressure and let the machine cool it then has a vacuum on the differential.

Will this pressure become a problem later with it wanting to force fluid around the seals and leak? On the other hand would the vacuum lead to contaminants being drawn into the seals? I was leaning towards a breather vent drilled and tapped into the fill plug/bolt to equalize the pressure as trucks do or would this let moisture in the air contaminate the differential.

Kubota recommends either their Super UDT2 or 80W-90 gear oil in the differential. Would gear oil cause less pressure to build? I do not foresee a difference as there is only a certain amount of fluid (2 gallon) and air in the system? Could someone with more experience comment on fluid choice, as I was thinking of going to gear oil, but then the rear end runs in the UDT fluid as does the transmission.

This tractor needs to last 70 years or at least until I get time to restore the old Ford 640.

When I had to replace the front wheel bearing in mine the dealer recommend gear oil. Seams like
one of the assembly friendly moves to have one fluid. But I replaced mine with gear oil.

Been a dealer for 28 years. The original ones had a vent , folks drive off in a creek and water gets in so we went to what you have. First of all about the only folks that have the pressure deal is ones that run a lot in road gear or fast for extended periods. I HAVE a few customers that chose to drill the fill plug and insert a cotter pin to allow little air exchange. As for enough pressure to blow seals doubt that ever happens. When a unit comes in for the first service we always drain and flush fill with 80/90 gear oil. My units here at the farm I also add Lucas oil additive. Seems to run quitter. Hope this helps and hope you like your tractor.

I would try to find a clean way to vent it.

The pressure probably won't be a problem, but driving it into deep mud or water when it's hot can can cause it to draw a vacuum, sucking grit onto the seals.

Any way to add a hose to the fill or vent plug? Run it up high, turn it back down to keep water out, even add an inline fuel filter to keep dust out.

My lawn mower has gearboxes for the deck drive that are NOT vented. Somehow they are working ?

I wouldn't vent from a fill plug unless it was near the top of a gearbox s I would think as
pressure built it might force oil up the vent, vent from near the top. A vent hose could be run to
a small filter, made from a small engine air filter, higher up in the tractor some place.