1. Regarding the trans leaks:
It could be the trans pan. The last person to do the trans service might have over-tightened the bolts. They are not to be tightened very much; any over tightening will cause leaks.
The trans should not be overfilled. The proper method of checking its fill level, is to measure after the engine and trans are warmed up (about 20 minutes of driving), in park, engine running on a level surface. A level surface DOES make a difference.
Depending on how over filled it is, could make a difference.
2. Leaks a little oil...again, only a handful of drops. Does not smoke or burn oil.
Where does it leak from? If you car has its engine encapsulation pan underneath, it makes it harder to determine sources. One place to look is the right side of the engine, forward, above the exhaust manifold. See if you have a bit of weeping there. This could be an upper timing chain cover seal, a common leaking area. Not too hard or expensive to repair.
3. Rear end tends to feel a little loose at highway speeds, like its being blown side to side by the wind ..
The rear suspension has five links per side. The upper diagonal link can contribute to the symptoms you described. But other worn parts can also contribute, some more expensive while others not very hard to replace or expensive.
The rear sway bar bushings are cheap and easy to replace as are the vertical links connecting the sway bar to the rear suspension. On a 1988 car you can be sure the bushings are worn and most likely the links as well.
Further, do the front sway bar bushings as well. Again easy and inexpensive and the results are great! (No link on the front) This is something a non-mechanical person could do. I did this on all my cars.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)