My Igus Drylin Bearings Shrunk

I replaced the LM8UU bearings in my P3Steel printer about six months ago with Drylins for a quieter life. All was fine until yesterday when I noticed the print quality had gone downhill pretty fast, on inspection, I found that the bearings had shrunk, the bearing surfaces were fine but the casings had shrunk by around 1mm compared to a new bearing. Totally weird considering the printer has not been exposed to any environmental extremes or chemicals apart from the odd bit of alcohol and hairspray.

I've just put the original cheap chineese bearings back and the print quality is better than ever but the swishing noises are kinda annoying, is there a quieter linear bearing or should I reprint everything for phosphor bushes? I'm done with plastic bearings for now at least...