You may not need to replace your sticky cup mount if it won't stick.
We use a two-part system to get the mount to stick. The first is the shiny ring around the flat middle part. That's a tacky silicone ring, and it's why we call them "sticky" cups. Second is a locking lever that forces air from between the cup and the windshield.
First, inspect the cup for deformities that may cause the vacuum seal to break. Micro-cracks, scuffs, and any kind of hole in the suction cup can cause air to leak out and break the seal. Deformities are non-repairable and mean that the mount needs to be replaced.
If there are no deformities, you may be able to restore your mount by carefully washing the cup with warm water. Don't use soap, any chemicals, cleaners, or abrasive sponges. Rather, simply use your clean hands and water, removing any dust or debris with your fingers. If you have water that leaves behind mineral deposits (water spots), you might try giving it a final rinse with distilled water.
Once you've gotten the dust and lint and debris cleared away, shake off as much excess water as you can and let the unit air dry. Do not manually dry it with anything.
When it's dry, it's time to clean the windshield and install it again. Make sure to wipe down the windshield with a lint-free windshield wipe. Usually alcohol-based wipes are the best. Put the mount up and let it sit for 24 hours if possible. If it doesn't come down, install the detector again. This resolves the "failure to stick" issue most of the time.
If the mount still won't stick, then the silicone may have lost its tacky properties. The mount will then need to be replaced.