what is this access pannel for?
WAG. Access to the drive chains.?
Welcome to the Forums! Glad to have you. Not familiar with JD but as Nige said probably access to the drive chains, drives or both. Definitively a problem there.
Exactly what Nige said. It’s an access cover, and yours is leaking because of a stupid rubber gasket that never sealed worth a dam new from the factory. Pull the cover, clean the gasket surfaces really well, the use silicone to reinstall it.
Oil level should be at bottom of plug just in front of rear tire. If over full likely a drive motor leaking into the chaincase.
Those rubber gaskets suck but they aren’t designed to hold oil in that high. your drive motor face seal is out and your hydraulic oil/motor oil whatever you are using has leaked into your chain case.
Pull that fill plug to the bottom right of the cover and see if its overfill. The chain will sling grease all around the outside of yhe cover edges so a bad gasket seal will still leak, even from the top. If the case is overfill, draining it off will verify a leaking motor problem