Thanks, everyone. I have spoken to HO and they want me to try out my second jug first to see if it may be jug related as opposed to mechanical, so I'll do that next weekend and see what happens.
I had (what I consider to be) a bright idea yesterday. If it transpires that the problem is a "bug" issue I may have a possible solution. How many of you have seen indoor bird cages with a protective skirt
around the bottom to catch bird seed? I wonder if I got one of these would that protect the underside of the machine from further infestations? That leaves the vents on the ouside at the top free - I am still thinking about what to do with these. Do you think the 'skirt' will work?