Thank you all for your comments and suggestions.
The problem is definitely not the plugs (various) that I use, it is very much a socket issue and just one of the two. I don't think that I will use the WD40 route - I'll take it apart and if the solution is not obvious then I will replace it.
The problem is definitely not the plugs (various) that I use, it is very much a socket issue and just one of the two. I don't think that I will use the WD40 route - I'll take it apart and if the solution is not obvious then I will replace it.