When installing the gasket, make sure the thick side is at the bottom. Use a little plumber's silicone grease to lubricate the gasket and work it into place around the mouth of the the overflow body. The overflow pipe will have a little play (although not much) that should allow you to adjust its posi- tion and make room for the gas- ket.
Make sure it seats evenly for a complete seal around the connec- tion.
Replace the drain assembly and then fasten the plate with the two mounting screws to finish the job.