I've been doing functional ABS and ASA lately and had a couple very annoying warpage spots. One was a total failure. (We won't talk about the other 3 failures that were wet out-of-the-box Bambu ASA...)
The X1C is definitely nice, but the all aluminum-and-glass side panelling has a sometimes-unwanted side effect: thermal conduction.
The aluminum sides are so conductive that they do not allow the chamber temp to go above 40C, even after a couple hours of heat soaking the build plate at 100C before starting an ABS print.
Enter: One random bath towel. doesn't look like much but just covering the three sides with a thin layer means it's good enough insulation to get the chamber up to 50C now! And the ABS parts look better than ever- every C counts.
All filaments are sensitive to surface oil, but PETG in particular super sensitive to any oil on a build plate, just fingerprints are enough, plain pei sheets you can totally clean with plain dish soap and water, makes a huge difference.
Oh yeah. I'm religious about wiping down with IPA every print and washing every few prints on PEI. I just haven't printed with petg on this printer yet, my experiences were at my college where you'd get 20 boneheads slamming nozzles into the bed, printing with way too high a temp, printing TPU on satin sheets and zero glue stick causing it to bond way to strong and literally rip chunks of pei off the Prusa plates... they were in pretty bad shape.