Atomic Man,

Not sure what planet you live in, but on the USA cars. The driver's side of the transmission is device called the modulator, and it has an adjustment also a vacuum line. Disconnect the vacuum line for its continuous path, and the presence of vacuum. If oil dribbles out of the modulator from the nipple you need a new modulator of the same color. You can attach a vacuum hose test the modulator with a vacuum tester, or suck on it your self for leaks or actuation sound.

Yes, The B2 is the culprit too, and the culprit is the inner black seal of the B2 seal.

Here are some threads that can help you:

DIY W201 Transmission Modulator Removal, Replace, Trobleshooting & Common Problems - Mercedes-Benz Forum

How to Replace Your Oil Cooler Lines

Hope it helps,

Martin