Heat riser stuck

The purpose of the heat riser is to help a cold motor heat up. In Florida where you live, the heat riser would hardly ever operate, if at all. Motors get up to operating temperature quite quickly. Up here where winter temperatures are substantially below freezing, the heat riser operates regularly. Unlike you, I've found very few seized heat risers. If it's seized, it'll be seized open. For all the good it will do, you're better off just leaving it be.