I'm gonna say its time for new cases... That sucks though man. Remember to keep up your maintanence of the crank aswell, alot of people think that the piston is the only thing they need to worry about. Rule of thumb for 250s is usually about 3 pistons to a bottom end. You can go more than that, but if you're racing and riding hard I wouldn't recommend it.
If I were you, I would hit ebay for a couple of things: Left crank case, right crank case, and a clymer manual for your bike. Then hit up rockymountain atvmc for a crank kit aswell as a case splitter if necessary.
for the love of god, don't just get rid of that CR. Repair it, and keep riding it, I would kill for one and so would alot of other people. Fantastic year for the CR.