Use of words

Doubt - to be undecided or skeptical about; to tend to disbelieve; distrust; to regard as unlikely
e.g. I doubt that the pan-democrats will resign; I doubt that we'll arrive on time.
Suspect - imagine; to surmise to be true or probable; to think (a person) guilty without proof
e.g. I suspect they are disappointed; The police suspect him of burglary.

Both leak and leakage are nouns. The meanings and usage are different.
Leak is also a verb. Meaning: to enter or escape or allow to enter or escape through a crack, hole, etc.
Leak (n.) - an accidental hole that allows something (liquid or light etc) to enter or escape;a hole or a crack; a disclosure, often intentional, of secret information.
e.g. a leak of Government plans; a gas-leak; one of the tires developed a leak; pls fix the leak in the roof.
Leakage - an act of leaking
e.g. a leakage of information; Leakages in several water-mains had been reported.

2009-11-26 14:35:24 補充：
Doubt - to regard as unlikely
Suspect - to regard as likely