I only clean what I can reach with the stitch plate off. I do take a pipe cleaner and swab lint out from pretty deep in the machine's workings, but I don't disassemble it any further than taking off the stitch plate and removing the bobbin casing.
I don't oil it, either. I have a Janome 6600 and my dealer said it only needs to be oiled once a year, which they do for me at my annual cleaning/check-up.