Diff Fluid - Factory or Changed Already

[ed1948]

86 MCSS, 90K miles, G80.
I spent 20 minutes(!) removing the diff cover. A few bolts were very tight,(snapped one 13mm socket when I used my 2 foot Johnson Bar!) and the cover used only sealer, no gasket. The filler plug released fairly easily.
Did an OEM installation used gaskets or sealer?

Can the color/condition of the fluid indicate what the health of the diff unit is?

 

[pontiacgp]

GM used gaskets, Ford used silicone. Sounds like someone had the cover off and over tightened the bolts when they put it back on