Mitsubishi MTE2000D, Dig It 258 Mini Ex, Deere Z930A ZTR
Valley Power has a parts diagram online that may help you out. Satoh Parts
I have had a similar issue and it was the upper thrust bearing (part #3). There is an upper and lower and it is not uncommon for them to go out. Valley Power ( http://www.satohparts.com/) will have the part. That is not to say that this IS your problem....you'll have to investigate but it is likely the culprit or a similarly easy fix.