Where did u get the ABS cement?
Any good hardware store has ABS cement. Do not get the cement that does it all or any other cements. Just plain and simple ABS cement.
I removed the fender (easy to do ) roughed up both sides with a fine grit sand paper and applied glue and held them together with tape and something heavy over night. The 2 pieces will in effect be 'welded' together forever.
From Murph' website: While the best installation results will occur by removing the fender, it is an operation that can be done with it in place also. Clean under the back lip of the stock fender, using paint thinner or alcohol. Give the Murphs' Fender Extender a good swipe of ABS glue, let it set for about 45 seconds, then stick it to the fender. The unit is pretty much “stuck" after one minute of holding in place. For best results clamp the pieces together overnight. Full cure time is 24 hours.