Clark crystals aren't great on a cartel case. They distort the rehaut too much. After trying many different options, the best rep version I've come across is the CWP crystal, however they do seem fairly brittle. I installed several on my 5513, after a while hairline fractures would appear in the area between the case and retaining ring. The crystal itself was a snug fit on the case and the retaining didn't need much pressure to press into place. So after several tries with the CWP, I went for a used T19 service crystal instead, which hasn't given me any problems.