It just so happens that I have a timecutter in here now that has a case leak! The left drive is a Hydrogear #ZC-DFBB-5WA-3CPX
The right is #ZC-AFBB-5W5A-2CPX. What are your numbers?
There is no gasket as I have torn one down in the past. If that is similar to yours, you will need to remove it. Remove all the case bolts and "carefully" remove the case. I say carefully because of the thrust washers that "might" adhere to the case by the oil. Clean all the gasket material off of both pieces. Don't button it up yet as I am waiting on a reply from Hydro gear about "filling with oil and what kind, and capacity. It just might be easier to fill with oil while it is apart.