artially cured or blended to increase its molecular weight to at least about 13,000 and its viscosity at 25 DEG C. to at least about 6,000 poises and which has been compounded with a mixture of fibrous and non-fibrous fillers, extenders, curing agent and other ingredients to form an extrudable, semi-cured, curable resilient polymeric sealing composition which is extruded to sealing strip form, whi