Lucas Transmission Fix is our top pick and the best additive for slipping transmission. The non-solvent formula is effective and reliable when it comes to dealing with issues related to performance. This transmission treatment gives car owners the best of both worlds in terms of quality and price with a 24-ounce bottle that will give any car the tune-up it deserves. Lucas transmission fluid decreases the operating temperature and puts an end to foaming. The formula is also solvent free and is capable of drying up most seal leaks, however, it does not work on CVT systems. In terms of prevention, this additive allows vehicle owners to carry out preventative maintenance at an affordable price.