krkucan There is not 100% perfect way to have a motor checked. compression test of all cylinders and leak down check of all cylinders. Run a vacuum gauge to the intake manifold and check for vacuum reading and possible valve problems. Heat run to make sure all cylinders are running with in 200 degrees of each other.
A 10 mile road test and check for leaks, noises, and other sounds. If the motor has a solid lifter camshaft, this would be the only thing to come into question for a street car. How many miles ago was the motor built? If you have a good bore scope you can look into each cylinder and remove valve covers and check other parts of the motor. Make sure
oil is clean along with filter, feel
oil for gas smell or keroseno. This is about the most you can do without taking the motor for a break down and check. Over my 20+ years of asking questions and owning a cobra since 95, I have not heard of one owner selling his car that had problems that where hiden from buyer. I can't say the same for engine builder who sold customers motors with parts they paided for and not got them in their motors. This is why is so important to get EVERYTHING in writing before buying a car and all the documentation with the car and build.
Last note, It's hard to keep a cobra from leaking fluids. alot of this depends on abuse of the car, types of
oil being used, just overall assembly of a component. My motor is a rear main seal leaker. Replace and tryed different ways to stop this. Over time it leaks again. I am runing 1.5 quarts over full in the oil pan and this could be causing this issues. I wouldn't worry about little oil leaks, it's the same as owning a HarleyD shovel head with chain oiler. They know where you parked.
If you like the car, do the basic checks of a road test. After this anything is possible. Motors, trannies, rearends can all be rebuilt. Good luck. Rick L.