75 series swivel housing replacement

It will probably be due to the drive axle wearing the oil seal that is in the end of the axle tube, just about below the bottom shock mount.

When you remove the upper and lower pivot bearing caps, take note of the shims and where/how many etc. When reassembling, before you connect the tie rod end, move the housing from side to side and up/down. There should be no up/down movement and very slight side to side resistance.

Support the axle as you insert it, if you let it slide unsupported you can damage the axle seal.

Take note of the order of disassembly, many times I have found the swivel seal incorrectly installed.

If it is the left side swivel housing that is leaking the probable cause (since yours is a 75 Series & possibly done alot of mileage) is a worn bronze bush which is situated behind the oil seal which supports the axle.
This tends to wear on the bottom due to the axle floating when the hubs are engaged but the transfer box is in 2WD. This wear tends to allow the axel to rest on the bottom of the seal causing it to leak oil into the swivel hub. When you remove the seal after disassembly of the hub check the bush for wear.
I have found it is always the left side bush that tends to wear more then the driver's side due to the length of the axle being longer because of the front diff offset.
They are not cheap to replace. It cost me $90.00 just for one when I did mine hubs & that was 10 years ago!!!!

just take off the outer ring and turn it 180 deg ,put it back on . fill er up with grease and ahoy away you go