what causes transmission fluid to appear INSIDE the car, right side under carpet

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Pulled down carpeting on right floor side near firewall. Transmission fluid leaking thru? transmission plate? seeps along exposed hoses, stain on backside of carpet. Transmission shifts normal for now, not sure about codes. I"m not a mechanic ,love my 99 SL500 with 49,000 miles. Not listed as common problem. Cant find any info on MB forums. Was just discovered. Any ideas please! making me crazy....