Crossover pipe
 

I just received a new plastic crossover pipe for the coolant hoses on the front of the engine. It has the rubber o-ring type of gaskets built in. Do I need to add anything else to the area around the gasket when I do the install? I don't want any more leaks and I know my mechanic had to adjust the fitting of the o-ring gasket on the thermostat housing when it was replaced.

NO

I assume you mean whether you should add any sealant? Like Brutal said, no. I don't think there should ever be a need to apply sealant in the coolant system connections.

Replaced the crossover pipe today. Some of the inside plastic near the o-ring had eroded, causing a void. I assume the chemicals in the coolant caused the issue.