It doesn't hurt to run some Techron or Seafoam through your engine. A bit of carbon build up over time is somewhat normal, but a few things could make it worse. If you run short trips on cold starts, the mixture will tend to run rich. Same if you have a fuel map that is on the rich side, especially if you disable the O2 sensor and run open loop.
Most aftermarket cans need to be repacked periodically. 13500 km is a bit soon, but reasonable if your engine is running rich. Some mfrs offer repack kits for their cans. There are universal ones that'll work with most cans. Its basically fiberglass matting to replace old ones that load up with soot and other exhaust contaminants over time.
'18 Ninja 1000, '18 Street Triple R, '18 KLX250S, '15 250XCF-W, '14 K1600GT, '05 GSXR600 (track)