On the RDB, there are two silver flat head screws, one on top and one down by oil pump. Once they are removed the red cover will lift off, careful of any oil line etc as you remove it. Once the cover is off, looking from the back towards the top middle is what I can best describe as a black plastic boot with a black cable going from it to the control box, that is the photocell.
Worth a clean, but not convinced this will cure the problem as it seems a little too intermittent to be a dirty cell.
As I'm sure you are aware, intermittent problems can be a nightmare to identify, so its probably a good idea to start recording whats happening so as to see if a pattern can be identified.
If it has not been serviced within the last 12 months, worth while booking it in for one.
Worth a clean, but not convinced this will cure the problem as it seems a little too intermittent to be a dirty cell.
As I'm sure you are aware, intermittent problems can be a nightmare to identify, so its probably a good idea to start recording whats happening so as to see if a pattern can be identified.
If it has not been serviced within the last 12 months, worth while booking it in for one.