I rebuilt the 300E's (yes, I know it is a gasser!) vac system last summer... I think the PN in question is one on top of the HVAC box, yes? If so, I used the $6 kit there. If the real small one, then it was available then.
If you could show me a picture, I could help you further.
The Perf Analysis kits also work on E23 BMWs!