Replace old parts on the 8880 supercar

Hello guys ! I bought the 8880, build it , and i find out that the gearbox isn't working fluently. Aside this, i need to buy some white pieces that turn yellow ish. So i'm wondering if i need to buy gear pieces as well, and if it's better to use the exact same piece, or use new one. Like in the screen cap, replace the two conical wheel by the new double conical wheel ( I tried, it fits) ? Should i change the diffrential too for new piece ? Is there a website where i can find info about...