I agree, the design is poor
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- mine leaked at the top
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(opposite the bolt) too.
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I removed the mount from the pipe, bent it so the angle on the inside was just slightly more than 90deg and then refitted.
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This ensured that the gap at the top was sealed.
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It hasn't leaked in 3 years and I have no worries about any extra sealant/silicoln coming off and making its way through my engine.
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To echo above comments, use the orange ring too