Frank
I don't think it's a glitch or that something was changed in parts cost. But what was changed is the season calendar. As some tracks give a net gain, especially Monaco really helps your parts stock as it's extremely easy on the car, and some provide a net loss, with Monza being a notorious car killer with a hefty repair bill. So if your leagues calendar removed tracks that are easier on the car and saved you parts for tracks that cause more damage then your stock will shrink and eventually run out. Also a shorter calendar would be easier on parts than a longer one as the new car after the last race provides a free repair.
Thanks, that makes sense.