So there's evidence of a bit of BLACK oily mess BOTH at the vacuum pump output to the brake booster AND at the hose that connects to the shutoff valve. As far as I know, the VP and the SOV are the only two possible places where engine oil could enter the vacuum system.

I have the car back....my mechanic still suspects the VP.

I have the old brake booster line....need to slice it open and see what I find, although I imagine I'll find evidence of oily mess throughout.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 142k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife