Marc wrote:

Jeff: tip for the futu needing to pull the heat exchanger cores is
very rare. Just drop the end caps and use a 22 cal. bore brush.

DO NOT do this! At least, don't use a metal bristle. Heat exchanger
tubes are relatively soft, using a gun barrel cleaning brush will erode
them badly. Also the brush rod is a hazard to break the tube.

Use a thin wooden dowel to clean heat exchanger tubes.

DSK