I had same problem w/ RWS 48 & C mount base.
I cleaned screws & holes w/ degreaser, lapped rings w/ Brownell tool, used a screw as a ring/mount stop on top of receiver as well as built in stop on rings, upgraded screws w/ kit from AGE, wrapped one layer of blue masking tape around scope at rings. I took extra care to make sure rings & scope were aligned (using lapping tool) when mounting.
This was the culmination of doing a bunch of things piecemeal including not using the scope for a while.
The POI has remained solid for a year now.
One other thing is heavy springers can be sensative to hold. Some do better if held rock solid. Mine does better if held gently, but firmly & allowed to recoil.
I've never had this touble on any "real" rifle or pistol.
Very frustrating to say the least.