Thats Funny cuz...
Back in early december i had the trans on my 1992 300se (w140) rebuilt by AAMCO cuz reverse died and my regular driving (forward moving) gears are still shifting rough. Just like you 1-2 and 4-5 is rough but 2-3 and 3-4 is smoothe. They told me that they had not adjusted some pressure regulator on the trans. They put it up right then and there, showed me a beige plastic lever, about a centimeter big, and turned it about a 1/4 turn (dont remember which way) and voila! it worke. Smoothe as silk. If it is not taken care of, it is not a big deal, doesnt affect the life of the trans, just a comfort thing. Has to do with fluid movement. Just so u know, change the trans fluid ever 20-30k. Its worth it. Don't do it urself, its not worth the aggravation of dealing with crappy mercedes gaskets, spend the $150 and enjoy ur benz for ever.