pa-trick first off you can't clean a VW oil cooler out good enough to be certain that you have all the particles out. They are not a tube and tank design like a automotive radiator. they are what is called a labyrinth design like what is used on most heavy equipment "Detroit Diesel.Deutz Diesel and some Caterpillar" to name a few. You can try to back flush it if you want to. To do it I would use a non-flammable solvent like Stoddard's solvent but in a pinch even gas (DON'T SMOKE!)would do. but no mater how hard you will try it just can't be cleaned to the point where it will not release particles in to the oil. When I was in the business back in the 90's a company out of W.Virginia called Posi-Clean had a service where they would soak the contaminated cooler in a acid solution that was guaranteed to remove Babbitt"bearing" material but it would not remove other metals.It was OK for old out of date coolers that were no longer manufactured or a used cooler that you didn't know the history of and could not find new anymore, but this is not the case with a VW cooler. If you wish I can give you the number to Posi-Clean as they are still in business,the company I used to manage still uses them to this day. But the price to clean a cooler about the size of a VW cooler would run in the $125.00 to $150.00 range not including shipping. And with the damage that you had in that engine it would still not remove everything and they would not guarantee it. My point is any mechanic that would tell you (with a straight face)that he could clean it for $10.00 and it would be fine, is one you want to run away from as he is only after your money and doesn't have your best interest at heart.
66 Ghia, "Dexter" 76 flat window Beetle
It's not a Car it's a VolksWagon!