Presser foot sensor issue in July. They “serviced” the machine (which I did not request) and also cleared the warning problem. Sewed once in August, and sensor notice returned. Ordered a new part. Then the part that the control foot plugs into came loose and fell into the machine, so the jack drops out. Ordered that as well. Is it reasonable to be waiting this long for parts? I’ve called every 2-3 weeks. Was told a month ago “it’s tracking.” Better to go to another dealer? Not under any warranty, bought it on eBay. Can any repair shop work on it as long as they use Janome parts? Thank you. 

The 12000 is a recent enough model that getting parts should not be an issue. Since there is no warranty, it doesn't matter what dealer you take it to, even if non-Janome. For dealers not in the Janome network, parts may be a little more difficult to get, but I can't imagine a 4 month wait even for a non-Janome dealer. While I've got my suspicions about what's going on with your local dealer, I won't speculate. I don't think you have much to lose by going to another.

Thanks so much for your response. Not pleased with their runaround. May drop a line to Janome about this certified dealer. I’ll check around locally at other shops. Thanks again. 
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Alícia L