Trans Slow to go into gear and sometimes slipping - Line Pressure???
 

I've got an employee who has an E320 (1994) that has had issues with a slow going into gear and this morning is slipping a bit. He said it worked fine after that. The previous owners I think had something similar (wouldn't go into gear I believe).

He said the fluid level is full.

What could cause this? I'd guess that's line pressure? Maybe a pump or regulator or leak?

This sounds like possibly an internal seal that is getting hard and leaking more when cold. Still wouldn't hurt to check line pressure to rule that out as a cause, but you'll need to find the specs for line pressure and the location of the test port on the transmission.

Agreed.

If the shifting improves when the transmission (fluid) heats up, it is likely a hard seal softening up and sealing when it's warm.

You can try one of the Trans-X et al solvent-based addditives as a last-ditch effort to limp it along a little longer, but if the seals are going, it'll need to be rebuilt soon anyway.

i bought an 89 300ce it was sitting for a while,reverse takes about 3 seconds to full engage,so i added a bottle of lucas shift conditione,it helps with the shifting of gears but revers still takes its time enaging,i jus wait patientlyy,ther than that it shift pretty decent,light clank shifting from forward to reverse.