Mike, Not exactly the same engine as you are asking about but I have a pair of 3126B CAT engines. I have been told that the engine was manufactured with an after cooler which did not preform as designed and would eventually cause problems. This defect was detected quickly by CAT and a re-designed after cooler was developed. I understand CAT initially replaced the original after coolers with a newly designed one to owners at little or no costs. After a period of time, the replacement after coolers were provided at a reduced cost; but now, those with these same engines have to pay full retail for the new cooler AND a kit to install it. A cost around $6,625 each plus shipping and taxes. You are probably looking at $15,000 plus to replace. To be clear, this is my estimate and not a price from any source of parts or mechanic. I didn't realize there was a problem with this engine when I bought my vessel either. I have less than 1800 hours on my engines. After inspection by a reputable person I have been told that one engine is probably ok but one, which takes 3/4 seconds to start, is beginning to show signs of the problem that may be caused by the original after coolers. I've also been told that you can do an oil analysis and to possibly determine if there is a problem developing. My engines may not be in danger but that can only be determined by "looking inside". So there, you know what I know. Consider the source and I hope to also learn from our posts. If anyone has better info, please either post or email me and Mike direct. I'm sure we'd both appreciate "professional" help. Herb Seaton