Lots of discussion about this. Do a Search on Moryde blocks or some such variation. I posted some links below. Highlights from them are:
o - a crack larger than 3" long and 3/4" deep call for replacement.
o- Delamination is cause to replace
o - Call Moryde as they are great to work with and warranty the blocks for 9-10 years. They are also good at tech support and diagnosing whether your blocks need replacing.
https://www.montanaowners.com/forums...ad.php?t=54077 Refer to Post #8
https://www.montanaowners.com/forums...ad.php?t=74080
https://www.montanaowners.com/forums...ad.php?t=77315