'79 300D vac pump, anecdote and question

[unkl300d]

Hello, recently my 300D had periodic brake pedal stiffness and once it would not shut off immediately.
After checking the tightness of the vac hoses etc. I immediately brought it to my mechanic who immediately diagnosed the vac pump diaphram.
Normal wear and tear issue.
My vac pump is the early type with a diaphram not the valve.

Anyway, after changing the diaphram, it operated well...so far.

We found oil in the main vac line that goes to the brake booster (oil at the brake booster end) and of course there was oil on the worn diaphram of vac pump.

He squirted a bit of brake cleaner down the main vac line after disconnecting it from the brake booster in order to clean out that line of oil while the engine was running.

I later checked the shut off valve line and it was clean of any oil. The other lines were free of oil.
Prior to that, the mechanic did not believe there would have been oil in those other lines. I had asked whether I should replace connectors etc.

So much for the anecdote for the archives.

Question is, where did the oil come from that was on the diaphram.?

Should I be aware of any possible oil issues in the other vac lines even though I did not see any for the most part?

Thanks

Denis