Blue water bill!
Maybe you can shed some light on this. I asked this question regarding over size pistons for 15HO-30 many years ago at the community.
The replay at the time was rather evasive. So I asked again this year, but no replay at all.
Seems a bit rich to have to replace the whole cylinder/crankcase when a simple rebore could fix a seized engine...
At this time there are no oversize pistons available for the 15HP through the 30 HP. You may notice that various other makes of outboards also do not offer oversize pistons on many engines. With labor costs and liability, the rebuilding motors by dealers is not often feasible with today's high-tech engines.
"There is never just one thing wrong with a boat";
-- Travis McGee, main character in a book series by John D. McDonald
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.