Drayton scr?

My Drayton SCR seems to 'go to sleep' for no apparent reason. No lights at all, no green light when I press override.
I took the SCR off the mounting plate, replaced it and works OK - for a week. Now same problem again!
So once again, removed SCR from mounting plate - checked for mains voltage on mounting plate - OK. Bent contact fingers on mounting plate so that they grip the pins well and it's working again now - but for how long, I wonder?
Can this be a capacitor problem?