The SAE J2643 is a Elastimer Compatibility test for seals. Wen working with companies such as Cat, GE, EMD and other engine manufactures, this test is required to show that the aftermarket additive being added to the lubricant does not effect the rubber seals within the engine, such as rear main seal, valve stem seals, or any other exposed rubber component. Chlorine additives have been shown to harden, crack or in some cases expand seals causing leaks or failure to seal properly.