I just finished assembling my Rostock max, so my first print was the PEEK fan holder. The printer did an awful job with the print, the overhangs on the "wings" are a globby mess, the bridges on top barely formed, and the interior space is too small for the fan. This is with stock MatterControl settings, except the flow rate is 75% and I dropped the extruder temp by 5.
Then, when I was priming the nozzle for another print, I noticed something that didn't look right.
Why is the extruded filament grooved? Well, it looks like the nozzle is cracked.
I couldn't really get a clear picture (even by holding a magnify glass over my camera lens

http://seemecnc.com/collections/parts-a ... ard-nozzle