AGR gearbox leak

I bought my SuperGear2 about a year ago, and recently it has developed a leak from the front end cap mating area. I've tried looking for the replacement O-ring that fits on the cap, but the dealership diagrams & parts descriptions are so ambiguous. Does anyone know the part # for this? Also, is that all that I should be concerned about (anything else that should be replaced?) I didn't realize how problematic these things were, and of course the warranty is long gone, so I want to make this thing work!

Thanks,

Kurt