I'm sure the custom ones fit better and likely to last longer. I've used the accordion folded type and the spring loaded round ones. The foil-faced accordion type will definitely outlast the spring-loaded type, which are lucky to last a little over a year before they start to flake and disintegrate. I'm talking about a continual use. The spring-loaded ones are just easier to store.

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Sam

84 300SD 350K+ miles ( Blue Belle )