Mine is one of the first year's production, so I'd guess there is a nipple back there.
But I'll be damned if I can figure out how to grease it. I tried this morning just to feel it and failed. Even if I could have felt it, there would be no way to get a grease gun on it, unless they make a flex hose with a right-angle head.
Since I'm the original owner, I know it's been 25 years without grease. The front zerk gets greased regularly.
If it has two zerks, are they both on the same side?