"nb->mb is just a run of the mill assimilation. It's very hard to pronounce [nb] (alveolar nasal + bilabial stop) and very easy to pronounce [mb] (bilabial nasal + bilabial stop)."
I remember that when the site... common ground? or something? still existed, I sent jd420 a message about this np -> mp change: with m or p we need only the lips, with n we need the tongue too.
When I have become older it has become easier to say "I don't know" or "I don't know how to answer"; the latter means that you have read the message, duly noted it and agreed with it, but you don't have anything to add. That answer is better than not answering at all.
When you get older, you have less strength for everything, even for answering. I think that some time ago I posted a message wondering how I could cut down the number of my daily duties. I cannot quit walking, 55 minutes a day, sometimes a day off, or thinking, because without thinking (of those things I have already mentioned) my existence feels totally meaningless. The other things... They are not as necessary.
I try to retire more and get more relaxed.