Mazda Repair: 626 thermostat replacement, soft seal, imperfection

Question
is it always necessary to use sealant ont the gasket when replacing the thermostat?

Answer
This practice varies from tech to tech.  I always use a extremely fine smear of Ultra Black on all cooling system part changes to back up the new gasket.  Inevitably some imperfection in the mating surfaces will exist, the sealant addition insures the soft seal.