Gidday NL
On thinking about Oswina's rear diff. I reckon that it was over-filled (with fairly nasty looking diff oil - or it was diff oil once upon a time ... ), and this was causing it to throw oil out the breather, specially when under stress (like tackling the Gentle Annie Track ... ), making the diff housing look as if it was leaking at every gasket.
Maybe wash the housing down with degreaser, then see if any more oil leaks out?
According to the Haynes Manual, the oil is supposed to be at the level of the bottom of filler plug hole. Yours bled quite a bit out of that plug hole after the filler plug was removed. No water in the oil, ergo the diff had been over-filled at some point. It wasn't enough of a slope to cause that much oil to spill, IMO. Perhaps it was facing downhill (e.g. on chassis stands at the rear?) when filled originally?
Sorry I couldn't be more practically helpful today, but I wasn't exactly dressed for the occasion, was I ... :lol: :rotfl: