Product review (5 stars): You really can install this yourself!
Fit like a glove.  One piece of installation advice: when stretching the ring clamp around the outer surface, you MUST hold the ring as close to the gasket as possible.  If you pull it away from the gasket to get a better grip, it will peal the gasket off the seat and you will need to start over.  Instructions mention this, but it needs to be emphasized.