Ahh yes. I finally had a chance to look at our turbo specifically and you are right. They do not use 2 individual copper washers BUT it is the same principle regardless. A crush washer or gasket sandwiches the banjo fitting either way. The question is though.... what material gasket is GM using and is it re-usable? If it's anything like any other normal banjo fitting washer, it is not. Here is a pic of an example off of our car.

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No you need some sort of way to seal both sides of the fitting. I honestly can't see how or why a copper washer wouldn't work just as good as what GM is using, but I would find out either way if the gasket they use is re-usable or not. I would have to guess it is recommended to not be re-used, but I can't tell you for sure. I can tell you however that any other banjo bolt washer should never be re-used.

exactly right.... no matter how GM does it, you need BOTH SIDES of the banjo fitting fitted with some sort of a crush washer. Otherwise it will never seal correctly.

 

i ordered a new banjo and the gasket that goes with it so hopefully that solves the issue but of course it has to come directly from gm so it will be a few days before ced even gets it

 

I order from GMPartsEast, they always seem to get stuff to me pretty quick.