I want to make sure my diff oil is nice and clean and the diff is full. looks like its been breathing some out recently and a slight knocking at 30 ish (not audiable above this speed)

its a 3.62, but does it have a drain plug like a sump? or do i have to tackel the casing?

any advise would be great.

You need tp take the the back cover off and run/suck all the oil out.
The knock may just be backlash. Knocking has nothing to do with the oil however old it is unless theres none in there!

There a filler screw on the backplate.
Mines been seeping oil out for 2 years but every time I check it and try to fill it , it's full enough!

I can wipe oil from my case yet it is always full some how! If you split the diff you will need a new gasket I take it?

No gasket used on the diff backplate to body joint!