I have had good success repairing the silicone grommet with Permatex Ultra Grey RTV silicone sealer. Clean the grommet squeaky clean then apply the RTV sealer from the inside to the split area. A thin coating works well. Let the RTV ‘cure’ for 24 hours. When installing the grommet to the valve cover oil return nipple, secure with a small white (mine are milky color) cable tie. Cut off excess tail of the tie and turn the ‘knot’ away from view. Use a second cable tie on the upper portion of the grommet to secure the grommet to the tail section of the oil return tube(from the bottom of the turbine housing) also. I had found that the oil return from the turbine housing will make a oily mess, over time, in this area, even with a new or good grommet. The cable ties solved my problems.