This is all ridiculous. The fuse leaked and the fuse blew. One thing may relate to the other but not necessarily. There is not much engineering in fuses. The filament needs to be sufficiently thin to blow with at the rated current. If it is slow blow there needs to be some heat absorption to allow for surge currents. In some fuses the filament is designed to be exposed to air and in others not.
ULs is a for profit company and, of course, sells its services. Having retesting of fuses would cost money as would certification of an audio component. This is why you don't see these labels on much audio equipment. Designers can roughly calculate what their circuit should draw and try a fuse with just above that value. They then can see if it works. If they blow many fuses, they go to a higher value, unless they find a problem with their circuit. Obviously too high a fuse value may allow overheating of the equipment and the potential for a fire or a safety issue.
ULs is a for profit company and, of course, sells its services. Having retesting of fuses would cost money as would certification of an audio component. This is why you don't see these labels on much audio equipment. Designers can roughly calculate what their circuit should draw and try a fuse with just above that value. They then can see if it works. If they blow many fuses, they go to a higher value, unless they find a problem with their circuit. Obviously too high a fuse value may allow overheating of the equipment and the potential for a fire or a safety issue.