azhari,
I will follow your advice & replace the FPR, since other members seem to think that is the problem too. Depending on the cost, I may also replace the OVP as suggested. Then I'll try it out; if it doesn't recur for at least a couple of weeks, then you've nailed it; 'cos like you said, sometimes it occur once a fortnight, at times maybe daily. Thanks a million for the trouble to post the picture; for a person like me who is not very mechanical minded, that is a big help too! Will keep you all informed on how it is going.