First of all................Welcome to the Forum.
Bleeding the Clutch has to be from the bottom up, IE from the Slave Cylinder.
The Factory Shop manual (FSM) states to connect a hose from the R/F Caliper bleed Nipple over to the Slave Bleed Nipple.
Open the Nipples, and pump the Brake Peddle. (Do not pump the Clutch peddle) you are cycling the fluid from the Reservoir, to the R/F Caliper, thru the Slave Cylinder and MC and back to the Reservoir . This pushes the air up, air just does not want to go down for some reason.
Another way is to use a clean Oil Pump can, fill it with Brake Fluid, connect it to the Slave Cylinder and pump away.
here is a good video explaining it.
BMW, VW, Porsche Clutch Bleeding - YouTube
Bottom line is, you probably still have air in the system. you are not the only one pulling your hair out, there are a lot of bald headed guys that have come before you.
The Clutch (if you need one) is not all that difficult to DIY.
PeachPartsWiki: Clutch R&R
I know the 4-Spd trans on the 82 & 83 240D weighs 54lbs. Its an all one piece aluminum case. your 77 thru 81 is the two piece, with the iron box and the separate aluminum, Bell Housing. it weighs just a bit more. not all that difficult to DIY at home in the driveway/garage.
I swapped out the auto trans in our 85 for a 240D 4-spd here at home. Noot that big of a deal.
\This would be a good learning experience for your son, and he might have more respect for his car, that now he can say "I did that".
Post where you live and maybe a Forum member is some where close by that has done this before and will lend a hand.
Charlie