See my very recent post above yours. The current CAT recommendations are for inspection/cleaning every 2 years or 1000 hours and replacement at IIRC 6 years. This was not the original service schedule for most CAT marine engines but was added after many aftercooler failures resulted in costly engine rebuilds - but my original service manuals I do believe called for inspection/cleaning every 2 years or 1000 hours. CAT very clearly has updated the aftercooler servicing requirements some years ago mandating replacement on a regular interval, and I can attest first hand that the interval must be followed. Both times I replaced my aftercoolers there were initial signs of leakage - this was at 11 years of age and 8 years of age.