That looks like a rotary injection pump to me, but I'm not familiar enough with it to offer advice other than did you try to tighten it? I'm sure others will chime in soon.
VERY similar to the leak from one of the levers on my Perkins 6.354 CAV injector pump. I had it rebuilt in a shop that specializes in that sort of thing. I've seen the insides of those pumps and I don't trust myself to put everything back together correctly.