'93 400e trans slips sometimes then it's fine
 

On the way home from Easter Sunday service. I drove about 3/4 of a mile (up to 25 mph), came to a stop and the car wouldn't move. The engine would rev, but no forward thrust, then a little forward thrust. Coasted along at 5 mph, but it in nuetral, revved a few time, no change, rinse repeat, but it in Low2 and it engaged, and was fine the rest of the way home, which included a stop and breakfast at my mom's house.

I remember it doing something similar when on our vacation, a little incline and first gear goes out. Car drove fine the 500 miles home.

I've since noticed a leak in the cooler lines and am wondering if air is getting into the system and causing foaming up of the trans fluid. Sound reasonable?

In fact both times this occurred after driving a little i.e. backing out my of the long drive, then not going into first gear, and today drive a little, come to a stop and not want to go again.

First thing you need to do is check your fluid level, condition/smell. If you have an air leak I imagine you would also have a fluid leak when it sits for a bit.

done that, smell thing, smells fine, color fine too. but I will check the level. seems to me the level was fine (or within limits last time) because the fact the the transmission performed flawlessly for the 20 miles home.

I have a 93 300E and my tranny slipped intermittenly at first as well. I checked fluid levels and they were fine. Finally one day it would not shift into reverse. took it to tranny shop and yes it appears this is how this tranny goes out, intermittenly at first from what I have been told. Had to have mine rebuilt $2200.

Make sure your levels are good! my tranny guy says to keep it at the 1/2 mark as the fluid expands as it gets warm so if you fill to top cold, it will cause your front seal to go out.

My advise .... Start saving for a re-build now!

In regard to mespe's original post, this happened to me about a year ago. I thought I was going to have to rebuild the transmission. I flushed it out, changed the filter and added Mobil 1 transmission fluid, along with a bottle of Lucas stop slip. So far, it has never acted up again. Maybe there was something stuck in the valve body.

That's what I plan on doing today.

Pistons that can be replaced without pulling tranny are a good idea. There are ceramic/plastic and when they crack sometimes the gears just seem to go out.