I have a 2011 FXDC and i got a leak. Know whats causing it? Is that a seal or vent?

 

Look like somebody converted your from mid controls to forward. That's a plug to cover the hole left behind by the old shifter shaft.

 

A plug with a seal.

 

What size seal should fit that? Theres no seal behind the plug

 

the seal for that should be on the inside of the outer primary cover

 

Just checked the Harley site on this install and they recommend a sealant around the hole, install the plug and wipe away the sealant. Could use some clear RTV and clean around it with mineral spirits on a rag. Don't spray it on, you could wash away the sealant. let cure for 12-24 hours.

 

Ahreed, it's above the oil line, and that shouldn't be continually rotating like it was when the bike had mid controls.