Mitsubishi Repair Problems? Ask a Mechanic for Answers ASAP
This comes from what we call "hard rubber". It means that the rubber o-rings inside the transmission have gotten hard and is allowing the internal fluid pressure to bypass the seal until the seals get warm and soften up and expand so they will seal. Just short of having to replace all of them (there are a LOT of them) you can buy a transmission additive that will soften the seal. I see you are from Costa Rica so i dont know what all is available there BUT if any parts store has a product called BG Transmission conditioner, it works REAL good. Just stop by your local parts stores and ask them for it or you could even order it from the USA if they dont have it.
They could also carry a different brand. Just look for one that says it will rejuvinate the seals and give it a try before spending a lot of money on a rebuild of the transmission.