How do you know when it's time to replace the clutch?
 

Recently I've started feeling my clutch on my 40k KM MY02 WRX is acting differently.

First of all it now seems to shudder. It's only started recently. I'm not sure if it's the common cold clutch shudder or if the clutch is going.

Second, and more importantly, when engaging the clutch (releasing the pedal) for the last inch or so of travel, it feels like it's slipping more than it should or did. The sensation is somewhat subtle.

With the clutch fully engaged, I can't detect any slip whatsoever. And I've tried full throttle in 4th with RPMs ranging from 3000-6000.

What I really want to know at this point is how does one know the clutch is due for replacement? What are the symptoms and what is the time delay before the car becomes undriveable?

Also, for the cold clutch shudder, is it possible for the dealer to get to it and then decide it's not under warranty and make you pay for the labor of checking it out?

Any info, opinions or advice is welcome. Thanks.

dont know if i can answer all of your questions, but...
the shuddering is usually not caused by clutch going bad. it sounds like the normal subaru shudder.
for the acting different, the slipping, it could just be normal break-in. are you just dropping the clutch fast, or slowly letting it out, or somewhere in the middle. clutch slipping is most noticable from a stop. if you gas it and let the clutch out fast and its failing, chances are that it will slip.
even with a bad clutch, it should still hold in 4th at any rpm when you romp on it.
the time you have to drive depends on driving style, it wont just be acting like you said one day, then the next day bunk out on you and not be drivable. you will slowly notice it getting worse, more and more slipping at less throttle.