The "prongs" which secure the pad in position tend to "relax" over time, I found the best cure for this was to warm them up and wedge something in between the prongs, then allow them to cool.
I used a piece of a locking mechanism from a Bell Fruit Eclipse cabinet, however as most people won't have a clue what that is, if you give me a few minutes, I'll pop into the workshop and measure it up.
Anyway the measurement of your wedge needs to be 25mm wide
Alf