3M 850 tape is the ultimate fix. It's a couple thousandths of an inch thick, so it adds practically no bulk. It is very sticky, and being polyester it will outlast the camera. A couple of yards will last several lifetimes, so "expensive" doesn't really enter into it. 3M 235 is basically black masking tape. It's paper, so both thickness and longevity are potential issues.
The liquid electrical tape is very problematic; it completely destroyed an otherwise salvageable bellows when just trying to patch a few pinholes. I have used the Tulip black fabric paint for spots that can't be reached from the outside, but cautiously and sparingly.
The one upside of the liquid electrical tape fiasco is that I got in touch with the Custom Bellows folks. They do a great job, but postage to the UK and back really jacks up the price.
The liquid electrical tape is very problematic; it completely destroyed an otherwise salvageable bellows when just trying to patch a few pinholes. I have used the Tulip black fabric paint for spots that can't be reached from the outside, but cautiously and sparingly.
The one upside of the liquid electrical tape fiasco is that I got in touch with the Custom Bellows folks. They do a great job, but postage to the UK and back really jacks up the price.