Likewise, I learned to drive on a manual but after years of driving in London as a Technical sales engineer and later as a specification engineer with the huge traffic jams, my left knee started to ache at the end of the day and also the clutch plate used to get so hot that by the end of the day in traffic the car became also impossible to pull away smoothly. The car would jump a lot, almost as if it was a learner driver at the wheel and after escaping the big smoke and hitting the open road again, the clutch cooled down and became normal again.
I did that for thirty-five years, and then I decided that upon being given just London area to look after full time, I asked for an automatic on my next car and all my knee issues went away after that. I have now been driving an auto for 12 years and I really enjoy it, but I suspect that had I not been stuck in London all day, Monday to Friday, then I'd have stuck with a manual box. That being said, I'll add this, as a person who has size 14 feet, most modern cars do not provide enough space in the footwell to accommodate such large feet on manual cars, and I was finding my feet getting slightly wedged under the adjacent pedal from to time, so that was a problem.