Well, inside the engine bay it could be the oil cooler or the oil breather. Those are the most likely. Underneath its likely to be the plate you take off the change the oil filter, or the valve covers.
coolant leak from wire harness
I remember the push rod tubes being a source of an oil leak.
head gasket or piston rings, have a leak down test done in it to confirm gasket failure
You could have a vacuum leak, a bad controller, a bad air door or an electrical problem.......
There are a number of reasons why your 99 VW New Beetle might be hesitating including overheating. Your Beetle might also have a leak in one of the fluids.
205.00 at the dealership
Be careful - some of these products can plug the heater core
P0442 (EVAP emission system leak detected small leak) It could be a pin hole leak in any part of the fuel system, from the gas cap all the way to the vacuum lines on the intake manifold. A service shop has a tool to pressurize the system with "smoke" to locate source of leak.
A common source is the Wiper arm pivot seals. Or could be the base of the windshield under the rubber weatherstrip.
It could be the crack (coolant) pipe, or thermostat housing leak. Have something that knows about the engine look for signs of coolant leak. Unless your oil is foaming, then it sounds like a head gasket leak.
The faucet had a leak.
This depends on where the leak is. A hose could be loose or broken or there could be a radiator or engine leak. The area of the leak needs to be found to be able to diagnose.