Very nice tool and good to have finally!
Some suggestions for future development:
a) Selectable background color
b) Window size and splitter positions are remembered
c) Car's list view on the left side with thumbnail and name side by side (maybe sortable columns with selectable specs from ui_car.json)
d) Field showing contents of ui_car.json
e) If possible some darker colors for scrollbar and dropdown list selector
Pretty long wishlist, I know, but the tool is already very good as it is - thumbs up! :-)
p.s.
for the scrollbar & the dropdown, i use the standard .net components (no other files to be distributed: only the .exe) ...and i don't know if i can change the colors without a long programmation.