Is it worth fixing the gearbox on a LEGO Technic Bugatti Chiron (knockoff)?

I built a LEGO Technic Bugatti Chiron (knockoff version). I followed the instructions carefully, but I’m having issues with the gearbox. In D mode, some gears don’t engage properly, there’s a lot of clicking/ratcheting, and power sometimes doesn’t transfer. In one gear it basically behaves like neutral. However, R works smoothly and all gears feel normal there. I also noticed that the grey driving rings sometimes only fully engage if I hold the model vertically, which makes me think it’s a...