may depend on your engine
Like you I only put on limited hours a year. I have an older 2qm15, which is original on a 1980 Hunter 33' purchased four years ago. This winter was the first time I had the mixing elbow off. After taking it off, I hammered the rust around the end of the elbow attached to the exhaust hose to enable fitting on a new hose. Other than that, the elbow was almost clean inside. I cleaned it as best I could at deckside and reinstalled it. I would recommend taking yours off for an inspection. Then, you will know what you have rather than guess.