I have a Craftsman 16.5 Kohler pro hydrostatic. After 45 min. to 1 hr. the trans starts slipping and making a grinding noise. I drained the fluid from the transaxle and it was a milky gray. Now I do not know what to replace it with. I was told to try 10w-30, so I did and to mower wouldn't even move. I if used 15w-50 would the thick oil help? Any suggestions short of buying a new mower would be appreciated. Thanks.