Q: Oil cooler on 2006 Mazda Mazda5

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I have been told by my mechanic an oil leak is due to the oil cooler. He told me the whole part needs to be replaced. Why not just seal it with silicone?
(1) Answer
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It's not possible to seal an oil cooler with silicone or any other sealer. Engine oil is hot and under pressure, if you seal it with silicone or anything else, it'll fail quick and you could lose your oil and your engine.
If it leaking, it's time to replace the cooler.
I have a Mazda5 and was told we have to replace the whole thing (not just the seal) at a cost of $460 just for the part. Any sugguestions? The leak so far is not too bad.
Not failing, there is a leak at the top seal. Mazda is telling my mechanic that the whole thing needs to be replaced.Can they not just remove the cylinder heads and reseal?