1997 MTD 18.5 hp rider mower - Transmission problem. While mowing, it slowed to a crawl and then started dripping chocolate milk colored fluid from underneath transmission. The fluid is foamy. This is a new purchase for me, brand new engine, used mower. Could it be that I only need to add fluid? Or does it sound more like blown transmission front seal (I think this is more likely)? If so, how to get to it, and what to look for?