NED, interesting. I thought the S3L was my series, not sure why. My freeze plugs are definitely on the right side. I also thought the 2615 was the engine that 'grew' out of the 23HP model from the older Mit. Cub motors. Does the heater work well, i.e. faster starts, not slow turning over? How does the freeze plug heater install. Is it tapped in with a hammer, like you would a freeze plug or does it somehow mechanically expand in the hole? Any leakage around it? Thanks.