Currently there is no such thing as a sealed transmission. In terms of adding a stop slip additive, you must realize that this a Band-Aid and in many cases makes things worse down the road because the primary mechanism of these additives is to increase the coefficient of friction of the fluid making the clutches grab faster. If you have burnt clutches already than you will casue them to breakdown faster as they become brittle when they burn. If you are trying to fix a leak, which they accomplish by adding swelling agents which soften the seals and fatten them up, then you may be okay. I would recommend either way, to fix the problem rather than rely on additives of this nature, which rarely provide satisfactory results over the short/long term. If you have the 5-speed, make sure you remove the right drain plug as it's neighbor is the anchor pin for the band. Good luck!