Just found this thread, same here on my s10 2011. Looks like it's spiralling up. I'll tell you more guys - half a year ago I was looking for part on the fog lights kit, and found a disassembled s10 owner that had spare ABS unit that time. I've just contected him and he said "yeah, I'm still willing to sell it, but only after the season will be over" - 'cause at the time this unit is installed on his own bike. I've asked him if he lost the rear brake too - and bingo - he did.
P.S. My unit had like ten times more dirt inside. Literally loads.
did you report it to NTSB?