JD 555G warning light question.

So I finally found a track loader, in fact I've had it almost a year now. It's a 555G and I love it. It runs and operates great. But now I do have a warning light that comes on and stays on for the most part. It is the "TRANS OIL FILTER" light. It goes out at times but mostly stays on. Can someone tell me what this means, what service is due, just exactly where should I go from here? Is it a matter of changing or cleaning a filter or is there more to it. It's an 1989 or 1990 model. I've attached a pic of the warning light. Thanks for any advice you guys can give me.