Oozing sore on shoulder?

I'll be calling the vet on Monday, but I wonder if anyone knows what this might be? I first felt it on Thursday night and it hasn't changed since. It doesn't look like an injury and it seems to be just a surface thing. Not bloody but sort of wet. No other spots on his body that I found. I don't think its causing him much pain bc he doesn't mind when I pet near or on the spot. He's acting totally normal and I haven't seen him licking it at all.

That looks a lot like ringworm. If you have a black light and shine it over the spot most likely it will fluoresce (although not all types of that fungus will fluoresce in a "black light").

Keep and eye out for more spots showing up on his paws if he is scratching, and watch for raised red patches on your skin as well.

Oh man, that's what I was afraid of

So Gussie spent the morning at the vet. The good news is she doesn't think its ringworm. It's possible but unlikely in her opinion. Unfortunately, she's puzzled as to what it is. Her top suspicion is a scratch from the other cat that he licked into a raw patch. She took two samples of skin and fur and we'll see if they grow anything in 10 or 28 days. As a precaution, she gave him Tresaderm for now and will change later if needed.

On a separate note, he's down to 14.6lbs and it's time to switch him from losing to maintaining! He's lost about 4 1/2lbs since May and his gaol is 14-14.5lbs. I'm nervous, bc this is the second time we've gotten him to this weight and maintenance is much harder. But at least he rid of all that unhealthy fat and I just have to be more strict with his food this time. I need my boy to stick around a good long while.

I'm glad he was checked out and it's looking okay

Keeping a healthy weight always seems much harder than actually reaching that goal (as most humans who have ever had to diet would agree *raises hand*).

I'm not sure how his diet is, but using treat balls to feed him part of his meals can help with weight loss and maintenance. Keeping a kitty active is always a plus not matter what their weight or health issues.