W140 (300SEL) vacuum system problems

Hi, I am a happy new owner of an "old" '91 300SEL.
The car is fine, but the vacuum system (central locking etc.) needs quite some care.
I know the previous owner replaced the vacuum pump unit (under rear
seat) recently, but it has already broken again.
It appears that the pump itself was filled with some oily liquid, and that the rotor of the pump mechanism was physically broken (splintered), probably because of overload due to the liquid in the chamber. I looks like the liquid comes from the transparent vacuum line, which is the manifold vacuum assist line from the vaccum distribution block and thereby from the vacuum system controlling the heating and A/C (which does not operate well either).
The car has facelift to W220, and the vaccum control of the headlights is therefor disconnected. I suspect the leakage may come from there (as one possibility), and I have ordered a Mityvac to troubleshoot the complete vacuum system further.
Meanwhile, is there anyone who knows, where the oily substance may come from?
And not least, does anyone know where to obtain a replacement pump motor/mechanism (possibly with a worn down motor) or the pump mechanism itself (instead of the bloody expensive complete unit)?
Thanks in advance.
/Jens (Denmark)
PS: I am new to this group. Please excuse me, if the problem has been addressed earlier (I couldn't find it in Google)
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I think it my be Auto gearbox oil. Check the gearbox vacuum pipes to see if any have oil in them. Then replace the part on the gearbox (either Modulating valve or the S/E & Cat warm up valve). Blow out the pipe and fit a new C.locking pump.

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Thanks, I will check.
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The central locking and heating vacuum system are mutually interconnected through the manifold vacuum assist line.
Does anyone know, which way the vacuum assist works (does the pump apply vacuum to the heating system, or vice versa)?
But as I see it, this system is isolated from the automatic transmission vacuum system, except that the two systems have their vacuum reservoirs in the same physical unit.
Of course, if there is a leakage between the two systems (inside the vacuum reservoir), liquid may be passed between them, and thereby from the automatic transmission to the locking system.
Is there an easy way to access the reservoirs, so I can check them?
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Once again thanks.
I seems like you are right. The modulator gets manifold vacuum directly (and cannot leak into the vacuum distribution), but there is two valves ("selection program") in the left side engine room, getting vacuum from the vacuum distribution block, and oil seems to come via one of them (from the black/red line).
This line goes to somewhere on top of the transmission. Is there an easy way to access the vacuum actuators there?
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