Briggs 19.5 HP Starting Issues

Hey y'all I'm new to the forum, this is my first post. I have a Briggs 19.5 HP OHV motor that is on a JD D110 riding mower. It was given to me by a friend. He said he was mowing and it began to run rough so he switched it off. He went back out later to try and start it and it wouldn't crank. So now it's with me to tinker on. The motor turns over but will not start up. It just spins. Model # 31P677-0236-G1 Serial # 100715ZD 88279

I have done the following so far,

Replaced old fuel with fresh.
Changed Air Filter.
Checked Fuel Lines.
Replaced Fuel Filter.
Checked Fuel Pump.
Checked Ignition Spark and it's firing.
Checked Valve Rockers for adjustment. All seems fine.
Changed Oil.

After all of that it started up and ran for a few seconds then stopped. Wouldn't start up again just spins. Then I noticed it's leaking gas (not gushing) from the carburetor. It's a Nikki carb 594603. I can't pinpoint exactly where but I can run my fingers across the bottom of the bowl and around the solenoid and gas is present. It's also throwing gas out of the muffler. No gas present in oil for now. So I'm unsure where to go from here. Should I replace the carb? Overhaul the carb? I realize an overhaul would be cheaper however I can't find an overhaul kit for that model Nikki carb because it has been superseded by Ruixing 594605. I don't necessarily want to spend $100 on a new carb if it's something simpler and cheaper. All opinions and advice appreciated. Thanks for reading I know it's long.

I had the same problem with my Walbro carb on a craftsman mower. I rebuilt the carb, added a new o-ring to the fuel solenoid and still leaked. I called Walbro and they said the seat inside was shot and I needed a new carburetor. Rather than spend $150 on a new Walbro, I found a "compatible" Briggs and Stratton carburetor. Looked identical, only one problem. The plug for the solenoid had flat prongs and the old carb had round ones. With a bit of patience, I soldered the connections. RUNS LIKE A CHAMP!!