I worked in automotive sealing systems (EPDM) for about 10 years. They are barking up the wrong tree. Shrinkage has always been a problem in sealing systems. There are simply too many variables. The polymer is just one of those. The amount of tension during extrusion, the amount of shear introduced during extrusion, the type of carrier (e.g., woven wire), curing temperature, the percent of cure, the formulation (e.g., reinforcing materials), the ambient environment on the vehicle, etc. That is why the automotive engineer designs the weather-strip longer than the opening to allow for the shrinkage. This is the type of question that comes from someone with minimal experience in the industry.