Head gasket leaking - no other symptoms- fix?

I've got a 2012 prius C; 135k miles. Never had a problem. Took in for an oil change years ago and the dealership reported a head gasket leak. I was shocked and didn't believe them. Took it to another shop, who quickly told me my head gaskets were fine. Well, years later, coolant is crusting around the perimeter, so I guess the dealership was correct all along ($4,500 est to replace head gasket). Still not showing symptoms. Is it worth getting the wheel speed sensor replaced (dealer quoted $1,800; intermittent loss of signal to RF sensor; CODES C1235 FOREIGN OBJECT ATTACHED ON TIP OF FRONT SPEED SENSOR RH & C1464 FOR FRONT SPEED SENSOR RH CIRCUIT) and driving it until the engine dies. Seems a better idea to replace the engine vs repair head gasket. Or should I just get something else?

 

These lights come on intermittently. And the braking feels stiff when they come on, but back to normal when the lights go off. Also the traction control light goes crazy, flickering and the wheels stop at different speeds when it's the sensor isn't working correctly, so my wheels serve while stopping unequally.

 

Slow loss of coolant

 

I think it's crusted along the split-line. I don't know anything about cars really. Wish I did. I am a DIYer on home stuff...