I have a Sears Lawn Tractor 21HP, 42in mower 6 Speed Transaxle that is leaking fluid fron the left rear wheel where it joins the Transaxle. The entire Rim/tire on inside is coverd in black colored fluid. What is the cause of this and how do you fix it?

That is probable 90w oil and your seal is shot. Do you have your manual and the complete model # like 917.22345?

Thanks for the reply, Model# 917.287210 and Parts Manual does say to Refill Transaxle with 10ozs. Of 80W90 gear lube. How hard is it to replace the seal? When looking at the parts diagram it's the last piece shown on end of Transaxle shaft so, guessing you have to take the Transaxle totally apart?