When did they switch from a flat top to a dished piston. I got the flat top kit for my saw. The Oem piston was $280 Canadian pesos. Another 20 bucks got you the whole top end. Go figure. Mine is a 2017 I believe not positive. My fish memory can’t remember what piston it has lol. I won’t have a chance to look at it until this weekend. Are they interchangeable?