1987 300td VCV/Shift question

[brooklyn]

Hey Guys, so still trying to chase down a hard shifting issue. Even standing still, shifting from reverse to neutral I get a loud thunk in the rear. Replaced the flex disks which I thought would help but now looks like I need to do the differential bushings as well...

As I'm checking vacuum, strange things are happening. I get 20+hg out of the pump consistently, and 15hg out of the BFS, but not consistently. I pulled the VCV (which is only a year old) to reset it and noticed some black oil inside the housing where the angled pin is. Does that mean it's leaking or no longer sealing properly? I generally test vacuum at the source and at both green dampeners, the VCV port sometimes shows vacuum sometimes virtually nothing. I don't get it, any help appreciated.