I recently read some papers on Kant's categorical imperative (McCarty, Kosgaard, Gressis mainly) on how to properly formulate a maxim according to him, and on the multiple problems linked to those things, and it seems to me as though there could be no way to salvage or solve the problems of the false positives or negatives one could seemingly derive at will from Kant's system, especially from the first formulation of the categorical imperative. To me, because it seems as though you could demonstrate anything be moral or immoral depending on how you formulate your maxim, even for a single action, which is contradictory, and that the diverse solutions offered to solve some of these false positives/negatives aren't very satisfying and often times, although they might indeed solve some of these cases, they also create new ones, Kant's moral theory seems to be shaky at best.
For instance, it seems highly problematic to me that you could split up an action infinitely and that although the components of that split up action might be moral on their own, that action when taken as whole might not ; so that if you were to take for example the maxim of ''always buying X, but never selling X because you like X'', then that maxim would fail the test of the categorical imperative's first formulation (if everyone could buy something, but no one was selling that thing, no one could buy it in the first place -- it is a self-defeating maxim). However, if you only take the maxim of ''always buying X because you like X'', then it can be universalized, and same with ''never selling X because you like X''. So depending on how you formulate your maxim, and purely on that, you achieve different results which are contradictory, which is problematic to say the least. Not to mention that this would be a false positive even if it worked out.
I was therefore wondering :
1) If anyone found a comprehensible and plausible solution following Kant's system on those problems?
2) If not, has someone found a similar system, even if only loosely grounded on Kantian principles, without the issues of false positives/negatives?
3) If not for both 1 and 2, is there any point to even studying Kant's moral theory, if it is so flawed? Shouldn't other moral theories be studied instead?
EDIT: the maxim should be read and understood this way : Always buying X and never selling X (action) whenever I can buy X (condition) because I like X (reason). My maxim should follow this way of formulating maxims If C (condition), then I’ll A (action) for the sake of R (reason).