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?