Shelter Cavy- Missing fur behind ears and sore on back?

We just adopted a new guinea pig from the shelter. He's about a year old, and the shelter said he was given in by his old owner. We got him as a future friend for my other, older male guinea pig. If we have to, we're willing to keep him in a separate cage if they never learn to get along. Of course, he's in quarantine for the next few weeks, and we're watching him for illness.

He's extremely friendly, and he even runs over to greet us. Unlike my other piggy, Popcorn enjoys being held and spending time with the family. He's much less independent compared to Tyran, our older pig.

Upon taking Popcorn home, though, we noticed a few things that we didn't see when at the shelter. He's missing a few tuffs of fur behind his ears, and he has a healed (or mostly healed) mark on his back I think might be a wound. Before, his fur was covering it, but I cleaned it up a bit and moved the fur to see it better. We're looking for a guinea pig vet (the one I know of recently moved) to have a look at him tomorrow, just in case. I took pictures, to see if any of you have any ideas as to what might have happened. To me, it looks like he might have been in a scuffle or something. My current guinea pig has never been sick or injured before, so I'm not certain.

He's a sweet, lovely little guy, and I want to make sure he's healthy, too!

His missing fur behind the ears:



And his sore on his back.



The sore seems completely healed over, but it still looks like a sore. Should we be worried, or just take him to the vet when we find out the best one still in the area? Should we be taking certain precautions? I've never had an injured pig before, and other than the wound, he acts extremely happy and ordinary.