An occasional spitting of the dummy seems perfectly justifiable. What does your surgeon have to say? As far as I am aware, a seroma differs from a cyst insomuch that it’s not an actual (benign) growth filled with fluid, in a seroma fluid simply fills existing pockets in the body, often causing discomfort by doing so. While most doctors like them to disperse naturally (wouldn’t we all?) lingering ones pose their own possible problems by providing a lovely haven for bacteria (which can’t usually enter a cyst). Your doctor should advise on options if it lingers. Best wishes.