That is a melted roller from the old Spectrum section. That entire unit can be removed and your trendsetter will still operate. Just unplug all the electronic connections and plug the two air hoses on each side and then there's just two bolts that it pivots on you can take those out and the...
Clean all rollers, the resistance motor wheel under the cassette, and the rubber part of the supply cassette spool with acetone. If it persists then one of the two (take up or supply cassette) motors has a bad encoder.
The Push To Be a More Versatile Printer
As the printing industry continues to evolve, printers face the challenge of becoming more agile and responsive to meet fast-paced changes in technology and the increasingly varied demands.