gear oil in the rear end differential of a 89 XLT Ford Ranger? (reg cab / long bed)

I will be changing the gear oil in the differential this weekend. Is there different rear ends sizes for the gasket and how much oil does it take?
Do you treat the gasket or put it on dry?

Reason for changing oil. It shows oil on the differential and it pops going from reverse to drive and it vibrates when coasting.

 

My new question: replacing the oil I thought it would go in the bolt on top but it appears it only hold the lines going across the top of the differential.
My differential (limited slip I believe) takes 3 quarts and silicon not a gasket.

 

I found where to add the oil. It is not at the top as I thought it would be. It is a pug not a bolt. It is located on the front of the differential about one-third of the way from the bottom on the driver's side. I will add it tomorrow. It looks like you use a ratchet to fit in the plug cavity to turn it.
That hole is also the correct level of oil.

 

Yes that is your plug. It is a 3/8's square drive and you will probably need a short extension to get in there. Also you want to fill it up till it is one knuckle below this hole. Put your index finger in hole and bend at first knuckle until you just touch oil.

 

At the Ford House they told me three quarts. Wrong! Unless they intended for two quarts and a squirt of oil.
Thank you, wheelsup68.
On Sunday I put in two full quarts less spillage . The bottles had a filler spout for a cap. Took it for a test drive. The Clunking from drive to reverse as almost gone away and improved on the reverse to drive but still there. The coasting vibration has improved. After getting home I squirted one more squirt from the third bottle of oil to be level with the filler hole. The vibration lessened even more.

 

You may want to take a look at your ujoints. You may have one going bad.