i got a replacement oil cooler from FCP groton,generally a good store. This is different from the original in that it needs another adaptor to attach to the oil cooler hose. At $44 extra,,its an expensive tiny pc of aluminum. it came w a rubber o ring.That doesnt seem to be right?? I would think it would be more secure w a copper crush washer??I think the rubber o ring would just degrade??Any ideas??

How about a photo for us? Starting in 1987, the turbo 740s used an extension to move the oil cooler to a place a lot more friendly for removing and installing the oil filter. The oil cooler extension used an o-ring against the block. On later cars the o-ring size was changed just slightly, and Volvo started using green o-rings made of a compound that is more resistant to heat. There is also an o-ring between the oil cooler adapter and the oil cooler extension. The only metal washer in the system is the aluminum washer under the head of the bolt holding the oil cooler extension to the block. I've never had a leak there.
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john