Leaks, leaks, ...
Stallion,
First of all the color of the leaking fluid will reveil the source. It could be red, green, transparent, brownish. That's the first step to get closer to the leak itself. Cooling system is relatively easy. If you use anti-freeze or true cooling fluid the green color will tell where it leaks. Gasoline is harder but the gas supply and return system is fairly uncomplicated. Check the gaslines for cracks and loose clamps. The gaspump can only be checked properly if the car is running idle. Check for dripping around the seals (first dry and clean it with a rag). Usually best is to replace the pump and seals, especially when the pump is old/worn out.
It gets harder when you're looking for oil leaks. Knows areas are the valve covers, oil sensor fitting, manifold seals. Leaks in these areas can be traced down by cleaning the area and powdering it with talcum powder. This stuff works great, it leaves white traces behind which direct you to the source of the leak. Shaft seals of both the gear box and the engine are harder to trace. The oil usually comes out of the flywheel cover. There is a little hole in the bottom that will tell you what kind of oil it is (red:gearbox, brown:engine). Don't be too hasty about replacing these seals, C3's always leak here. As long as you're not talking about large amounts just ignore and keep an eye on the oil level once in a while.
Another known source of leaking gearboxes is the seal around the shifting rod (left front upper side of the box) . Can be easily replaced and hardly involves any costs.
I said it before, I really appreciate the gearbox additives. They really help to keep your seals in good shape.
Good luck.
