Martin C. wrote:
UPDATE:
Apparently BrassCraft is Cobra.

I called Cobra customer support (800-835-2200) who explained that my
snaking technique was wrong, hence the kinks & broken snake.

Apparently Cobra doesn't sell the snakes directly because their
customer support said that I could pick up the 100-foot length at
Lowes hardware stores:

Lowes P/N 100817, 3/8 x 100 feet Slotted End Cable
Cobra P/N 90441, 3/8 x 100 feet Slotted End Cable

Cobra confirmed the 75 foot and 100 foot lengths will fit into the
BC400 drum, which is apparently called the "40 Series" on the Cobra
web site.

Cobra confirmed the technique is this:
1. Feed the snake as far as it will go
2. Then lock the thumbscrew (mine must be broken as there is no
plastic)
3. Then put it on forward
4. Then unlock the thumbscrew & feed again & repeat as needed
5. Use reverse only momentarily to back out of tough spots
6. When done, hand feed back into the drum

So, lesson learned!

The reason it kinked, they said, was that I was doing it all wrong.

I'd get a 1/2" cable if you can, much less likely to kink than a 3/8"