There's a black plastic line that runs from the round blue thing on the driver inner fender to the drive side of the transmission. It attaches to the top fitting that's not at the center of the round blue thing. At the other end, it attaches to a round metal device attached to the transmission just above the pan and ahead of the where the rod from the shift lever attaches to the transmission. There's a green cylinder about 2cm in diameter by 3cm long along the plastic line. Not uncommon for this line to be knocked loose during an oil change.
And of course there's all the other vacuum lines
Sixto
87 300D