my friend has 1987 300D with leaking trany and 1987 300E with less miles and no leak...can he swap them or these are completely different beast ?
Thank you.

More than likely, I think the only difference is the vacuum modulator pressure settings. Gasoline vs diesel. If you swap them from one to the other, that should take care of the difference.

However, depending on where is is leaking, it may be considerably easier to just repair the leak.

Here is some info that may help:
Index of /docs/mb/transmission

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )