There are dozens of quick bond adhesives on the market that claim to bond rubber.  After trying most, this is the product we found that works the best for a wide range of sealing elastomers.   (Not for use with Silicone)  (Ground Shipping Only)

Sand and Clean Rubber Surface for Best Results.

No recomended for critical sealing applications, but is very handy adhesive to make your own o-rings from o-ring cord for onsite emergency installation.