Took the differential out as part of my overall suspension, brake, etc refresh.

The dain plug had metal shavings

Does this look normal?

Also removed the differential mount and it looks good.

The new one is on the left. I was getting a clunk but found the differential mount bolts were loose. The old mount still looks good and was thinking to reuse it.

Not only were the differential mount bolts loose but so were the drive line bolts connecting it to the differential. Do these typically loosen up or was the PO/mechanic careless?

I do have a question on removing the differential cover. What is the best way? I don't want to injure it and it is stuck on good. I also have a potential problem in I could not get the upper drain plug loose and put on the mustache bar nut to the cover bolt thinking as I tightened that I could loosen the plug. Didn't happen but when I removed the nut it took the bolt out with it. I can deal with that but when I put the bolt back in, what is the best way to reseal it to the cover - threadlocker?

looks normal. This was mine:

I got the cover off using a punch. There are two extra holes in the cover that line up over the cover. These holes were somewhat sealed with grease and dirt so had to look for them and clean them out. I took a punch and tapped. I covered the end of the punch with electrical tape to not score the cover. I knew I had success as the sound of the tap went from a higher pitch to a lower pitch.

The diff mount can look okay but still allow quite a bit of movement from the diff nose. The clunk is from the nose coming back down (my theory). The diff is supposed to stop the nose from coming down too hard also (you can see a little bump of molded rubber between the metal pieces), but it gets compressed over time. If you look at the front metal portion of the mount when it's on the car, you'll probably find that there's only about 1/8" or less separating it from the metal cross-member.

If it's old and you clamp one of the metal portions in a vise, you'll probably be surprised at how easy it is to spread the mount apart with a screwdriver in the middle. The rubber gets weak over time.