Can you go into a dealership or to a quilt show at one point and have an FMQ on a different machine? That would reassure you that it wasn't YOU? :-D[/quote]
Well,things have moved on a bit this morning, because I did exactly as you suggest here. I had to collect my Mum's sewing machine, which I've just had serviced, so I asked again about FMQ. This time the dealer who in the past has told me it must be my fault almost admitted that the Janome is not ideal for FMQ. I tried 2 Berninas and a Brother machine, and produced not perfect but quite acceptable FMQ on all of them. I nearly cried when I saw the results - for so long I've been blaming myself and thinking I must be exceptionally incompetent: to see the stitching that I'd produced, with no loops on the back, was just so reassuring.
It's going to take a while to make the decision about choosing a new machine, but at least I now know that that is the right way forward. In the meantime I'll try some of the suggestions on here, including buying the bobbin case for the Janome, as I really don't like being defeated!