I purchased my Janome MC4000 in March of 1997. It was a floor model used for demo. The only time I've brought it in to the shop has been for cleaning and a couple of times for a "scare"...it was misbehaving. On one occasion, it was an operator mistake (needle inserted wrong ////blush////). The other time was when I machine quilted a quilt with high loft batting and had pulled the thickness along. I don't know the technical terms but my repairman made adjustments and I was on my way.
Lately I've noticed that there is a little tension problem that appears with certain threads. Haven't had that problem before. I use whatever threads I have in my leftovers. Newer threads seem to be "less substantial" than the older threads and I actually prefer them. I think I will "invest" in some of the threads that have been discussed on this board to see if I'll get better performance out my old baby.