If you just want to flush the origional oil cooler..... when I was doing auto repair we used to get a aerosol can of "trans cooler flush" and flush both directions then blow out with air.
I'm suspecting the stuff is still available You could try a parts store, if no luck try a tranny shop.
I would replace it with a large automotive transmission oil cooler, they have some on Ebay that have a fan attached. overkill? perhaps but better safe than sorry.
+1 on the tranny cooler. i put a farely good size one on mine and eliminated the factory one all together. i also got it out from in front of the radiator and moved it up on top of the radiator. now the radiator fan can draw nice cool air through the radiator. temp stays nice and steady now all the time plus its easier to clean the radiator now. i bought a fan off of ebay to put on top of the oil cooler that runs all the time.
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