You will see puddles on the pavement, color of fluid and location can help determine where it is coming from.
Also, to check cylinder head gasket, a compression test is useful. Low compression between two adjacent cylinders, will point to a blow in the gasket between cylinders.
Check for exhaust gas in the coolant, using a proprietary sniffer device.
mayonnaise like, white jelly, in the valve cover or oil filler, will point to coolant in the oil.
If the power steering rack is leaking, it is likely an seal or a gasket. Replacing the seal or gasket should stop the leak.
Replace the thermostat housing seal or gasket.
Gasket
look good
Don't do it. Or, check where it is leaking from, maybe just a gasket or seal.
If a transmission is leaking fluid, it is likely that a seal or gasket has failed. Replace the gaskets and seals and the leaking should stop.
Water in oil is usually caused by a leaking headgasket. This is the gasket between the engine block and the head. It is an expensive repair.
You'll see either fluid or grease leaking out of it.
Valve cover gasket? Prevents oil from leaking out of valve cover Valve seal? Prevents oil from entering the combustion chamber.
If you are loosing coolant, you have a leaking head gasket. If you are loosing oil and have a turbo, the seal on the turbo is bad. either intake manifold gasket or head gasket is leaking
A piston seal is a gasket designed to keep fluid from leaking around the piston. Piston seals are commonly used in brake calipers.
Failed seal, gasket, or component. Have the system pressure tested for leaks.