tuff torq k61 hydro's oil can be drained and new oil put in if you have an old model jd 100 or 200 series mower check to see if it's the k61 model if its not pulling like it should or is slowing down after mowing for a while it could be the oil needs changing tuff torq has all the info you need to get this done right filter is in trans and can not be changed my 94 model jd 178 began losing ground speed at about 450hrs changed oil ran for 2-3 mowings then changed again takes maybe 3 1/2 qts. changed oil again at 925hrs but had harder time getting air out of system than previous time but is running fine now just finished mowing my 1.9 acres and i must say i can not come up with a single fault to trade in mower for newer one in 17 years i guess it's become a good habit!!!!!!:cool2: