Heard back from Senn today. They will replace the part for free with proof of purchase within the 2 year warranty period (obviously as the HD 598s haven't been around that long). They said it will take about 2 weeks. I just hope they replace the part and not the whole headphone as I feel like...

I have had the same exact issue with my HD 598s. I picked them up when I was in Germany in December and a few weeks ago a crack began to form in the exact location as the posted picture. I left a message with Sennheiser a few weeks ago and did not get a response. I emailed them again this...