I also asked the guy and the shop about the leak, and they both recommended trying stop-leak before doing anything expensive. I picked up some Lucas Oil, topped off whatever was lost due to the leak (less than a quart so far, I checked it cold and I’m waiting for the engine to cool off to check it again).
DO NOT USE STOP LEAK IN YOUR ENGINE. Figure out what is leaking, and fix it. Any shop that is suggesting the solution to your oil leak is to put in stop leak is not a shop I would want to do business with.
This, 100%.
"stop leak" products are actually bad for the systems they're poured into.
Most of the time, they've got polymers, glycols or other chemicals in them that attempt to "soften" the leaking seal or gasket, or make it swell up.
Here's the thing, it'll stop a leak, for a little while... emphasis on the little.
Then the leak will come back, and be worse. Why? Because when that seal was either softened or swollen, said already worn seal was getting worn even more by the moving part either rotating or rubbing against it.
Cooling system stop leaks are even worse than that, frequently causing clogged heater cores, heater control valves, radiators, hoses, thermostats, etc.
Here's the good news:
You used Lucas.
Lucas's products don't actually fix a damned thing, and they don't hurt a damned thing. They're just thick lubricants that slow leaks by making the fluids themselves thicker. You'll even see me advocate their ridiculously thick red power steering fix in a bottle as the best way to shut up a Cardone remanufactured power steering pump for 70s-90s Ford applications, because it's the only thing I've found that does that.
The only bad thing about Lucas's oil additive is that it's basically gear oil, and lacks the antiwear additives that are in engine oils. If you used a quart or so to replace leaked oil, you didn't hurt anything, and there's no real need to hurry up and get it out of there, it can wait until the next oil change.