When i first got my car (about 6 months ago) it leaked coolant after shutdown, maybe 3 times and then the problem went away. Each time only about 1/2 - 1 cup of coolant. Recently (week or so) the problem returned only about 1/2 a cup and there is no smoke on start up and no hard starts. now however in the past few days i would estimate I have had to put in 2+ cups of fluid in every time i drive it and i went out this morning and started my now normal top off process to find it wouldn't fill, eventual there was coolant leaking from the overflow tank.

What causes these symptoms and whats the best approach to trouble shoot them?

At the moment I am planning on replacing the AST overflow and T-stat connector lines (aftermarket AST).

Any ideas?
Thanks
Jake