I think immediate washing is also a key. Just yesterday, I cooked a chilli, ginger, garlic and shallot mixture for a salad dressing, then washed straight away. I didn't detect any aroma from the lid or bowl and made a chocolate cake immediately afterward.
Argh... I'm of course having the same problem. I've only had the thermomix for 4 days and the lid and seal stink! I hate smelly things. I've cleaned with detergent, vinegar, lemon juice, bicarb. I've never left it dirty or with the lid on. It still smells like the vegetable stock concentrate that I made with the consultant. My DD's porridge that I made this morning had the lingering odour of it too I am really disappointed and shouldn't have to come up with all different methods to try to remove an odour or have to have a separate seal for savoury and sweet for a machine that is so costly and it is a problem that has been known about for a few years now. All this isn't helped by the fact that I have an extra sensitive nose due to pregnancy!