A couple of my P07s and my P09s have the flat MS cap. It can be a bit more difficult due to how slippery the plastic is, but it’s not really too bad. Lining it up can be a PITA though. What I really ought to do is press the tip of a small screwdriver into it after heating the screwdriver up. That would both give me a reference mark to how to line it up as well as give a small detent to make it easier to swap mainsprings out.