Thanks mate, what's crazy is that it's $1600 for one only haha, which I obviously won't pay. Very surprised as this mechanic is usually reliable. Also as you said it's mostly a cleaning job and I don't really think any mechanic would care and spend the amount of time cleaning properly, which highly increases the likelihood of a poorly done job.
I'm going to give it a crack I think. Crazy that it's been like this for years and it has not created any problem even after ignoring it for so long. It does not make a sound, it does not reduce my braking power and my front diff is working fine, Ive serviced the oil a few months ago. I used to look at it like an oil leak but yeah will get onto it sooner than later.