Number one. I fixed the problem with my switch, but I want everyone to know right off the bat that if done wrong your switch will probably be junk.
Number two. Does your switch look like the first picture?
The next two pictures point out the two parts of the switch that get stuck, preventing you from manually cancelling the turn signal.
In my stick figure drawing, figure one shows those two pieces with the signal off, and number two with the signal on. When the piece that looks like the numeral one clicks past the piece that looks like a slice of pizza, they get locked.
What I did was to take a razor blade and shave a VERY SMALL piece of the pointy end of the pizza slice off (figure 3). I CANNOT EMPHASIZE TOO MUCH that you start VERY SMALL, try the switch to see if you can manually cancel it, and if you still can't, shave a LITTLE more off till you can. Work on only one at a time. When the switch is in the off position, the overlap as shown in figure 1 keeps the switch in the off position. If you cut too much off, the switch will be sloppy in the off position, and if you have no overlap at all, it
may even drop down into the left signal on position just from the car bouncing.
This shaving operation must be done on both sides of the switch. I don't mean to the two parts I point out, I mean there are two of these sets of locks, one at the top of the switch assembly, and another at the bottom. Both of the "numeral 1" pieces can be seen in the first picture. The one at the top looks like a 1, and the one at the bottom like a backwards 1.