Has the truck overheated in its past??? This is typically a leading cause of head gasket failures.
The only symptom that is odd, regarding head gasket failure, is the anti-freeze smell with the heater on. Have you checked the coolant hoses that supply the heater core for leaks? Can you get into a position to inspect the heater core?
How do you know the ant-freeze is "leaking into the piston and is exhausted thru the engine."? What have you done for diagnostics?
I only ask these questions so you don't inadvertently lead Toyota to a head gasket repair when the problem could be elsewhere.
Suggest to just relate the symptoms to Toyota. Allow them to diagnose the cause and quote on a cure.