Here's my 2.7cents. I had cracking on my 300 mets, both sides and all the way round. I called Metzeller and they have a warrantee of 4yrs on theirs tires. You have to go through a dealer (basically anyone who sells them) and you can make a claim. The shop will remove your tire, call metzeller customer service for a 5 min conversation. They will fax them a form to sign and attach to the tire. Then Fedex will come pick it up. Then it should take 5-6weeks to hear back on how much refund you'll get back (dependent in tire wear I guess).
Now, I purchase a new tire right then (actually front as we'll) and got it mounted because I didn't want to be out of riding. I heard some places, if you purchased it from them, might swap it out and deal with the claim themselves. I purchased the cracked tire at another location so i wasn't doing the claim through them. So you could either wait for the coin from metzeller to discount the tire, or pay full and wait for a partial refund. I for one, had a prick or a time finding some one that a. can remove a 300 tire and willing to do the claim for me. Even the local Big Dog dealer didn't want anything to do with me, even though I said I would be buying 2 new tires and paying for all labor out of pocket. After my third message, speaking to them twice and being fob'd off I gave up.
Anyway, I'm still waiting on word from Mets so will see what happens.