spdrun,
Welcome to the hair-pulling club of MB clutch bleeding. With help from many posts here, I've probably got 15 hours invested in club membership dues.
Sounds like they actually got it to bleed right for at least a period of time, so air is getting in somewhere. Getting air in is unfortunately a leak somewhere in the circuit (slave, master, hardline between them, or maybe the soft line from the reservoir). Take a quick look under your driver's kick panel (you may not need to remove it to see) to check that your master is actually new AND dry everywhere. Then climb under the passenger side...actually, you can probably see it from the engine bay, and find the slave cylinder on the side of the tranny. There is a hardline that crosses over the top of the tranny, with a few connections that could probably go bad. BGKast had that happen to him, see link below.
83' 240D clutch just went out! slave cylinder?
My nightmare was I couldn't bleed the system, from above, from below, unless I backed out bolts on the the master and the slave several turns. Master was a crappy local part. Slave I actually bought here. Of course the slave failed 200 miles after the new master went in (you've already done the smart thing and replaced both at once) I must have soaked a quart of brake fluid into my clothes, my face and my driveway that winter...Good luck, ask questions.