Most of the muck build up is on edges - so the gaps either side of recording heads are holes that collect debris. Cleaning tapes have the job of removing this debris, and there is a very fine line between removing muck and removing metal and resin. There were wet cleaning tapes that tried to dissolve the dirt, then wipe it away, but they rarely did a good job. Worse is that the video and audio heads are proud of the surrounding surface, so the cleaning tape tends to be quite hard on them. Nobody ever produced a cleaning tape better than the junior engineer could clean them manually, with only a bit of training. In another topic I mentioned the kinds of machines they used in broadcast. Very often we'd haver them in a rack on pull out runners, and usually they would not have the top covers even on them. We had orange can Colclene - great stuff, the can said suitable for cleaning guided missiles - and was a blend of isopropyl alcohol and other solvents, and it evaporated completely, needing no residue. The procedure was a simple one on video heads (and MII video heads were expensive!) You never used fluffy cloth and never cotton buds - those little fluffy wisps of cotton would catch on the heads and you could snap them off if you moved them vertically. Horizontally, they were a little stringer. The rule was a lint free cloth. You gave the head a good swoosh, and as the liquid was under pressure, it softened the debris and flowed it away, then evaporated. You could also poke a finger into the cloth, squirt the tip and then rotate the bump of the head under your finger tip with a tiny bit of pressure. A bit more on the capstan, and a wipe of the guides and you were done. This was the same process on virtually any machine, analogue or digital with stationary or rotary heads. The real pain of course is the size. Video machines had space for chunky fingers. DCC never did. Some cassette machines made cleaning a cinch - others forced you to virtually dismantle them. Cleaning tapes were an obvious solution - even though potentially destructive/useless.