uhm well are you gonna pull your reeds out? because if you are just pulling your carb off the reed block, popping your gas line off and your throttle slide out to clean it you won't need anything. That is unless the little rubber gasket between the carb and float bowl is screwed but I've never had one leak when I've reused it. Some carbs have paper gaskets there and if this is the case you will need one... but I'm pretty sure a 2000 rm125 has the same carb as mine so I doubt it.