The oil is for the diff gears and does not go into the shaft itself. If it only happened after changing the oil I would suspect something to do with excessive oil level or the type of oil. Differential and not gearbox oil should be used, GL4/5 rated. There should not be a build up in pressure if the breather is working.
Otherwise perhaps it is just coincidence and a seal is leaking, but this is very uncommon, or at least hardly anyone reports a problem.