It's possible that the plunger tube assy spring is weak. I'm not 100% sure, but I think Ed Brown's "Hardcore" slide stop has the indent.
Regardless, it relatively simple to put a dimple in your existing stop yourself, if you are so inclined. If you're not, your local machine shop will probably do it in 30 seconds for free.
Regardless, it relatively simple to put a dimple in your existing stop yourself, if you are so inclined. If you're not, your local machine shop will probably do it in 30 seconds for free.