Shell Retinax G is a European specified formulation. You won't get it here in the US. I imagine any lithium-based NLGI 2 grease should do the job in this application.

I wouldn't use silicone grease unless maybe it was formulated with thickener. It's just not that good a lubricant for check strap application.

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95 E320 Cabriolet, 169K