Problem with Hayward Power Flo LX Pump

The gasket on the strainer lid wore out and began leaking water so we bought a replacement. The original gasket was thicker than the replacement but we tried it anyway. As predicted, it leaked. We took it back, along with the strainer lid, to show our pool guy. The gasket they showed as the one that was for our particular model is the one that leaked. We asked about one that was a little "fatter" and bought that. It fit just fine but the cover would not go back onto the strainer. We have tried everything to get it to go down enough to secure it back to the strainer but no luck. I'm not understanding what is up.