One of our cars, a Peugeot 206 developed a annoying fault in the seat rail that would't allow it to lock in place. I made a quick replacement part in Sketchup as I couldn't buy a new part anywhere (it's normally out of aluminium).Printed in PLA with 100% infill and support (in Cura).
I usually design things in Sketchup to print stuff on my UM1 or UM2. The designs are always accompanied by their source files for editing and a collada file for printing but if you want a particular format, just ask.