My roommate has a lovely 1985 740 Turbo Diesel GLE with an automatic transmission that she bought back in January: 175k, clean body, good engine. She took it to a mechanic before buying, who gave it a mostly clean bill of health (some hoses needed to be replaced, but otherwise fine.)

Now it's developed some transmission issues.
1) When cold starting the car, if you don't get it out of park *right away* and get it moving, it stalls.

2) Also with cold starting - once the car is moving, it takes a while to shift out of second gear. Mornings are a ritual of driving the car around the block for 10 to 15 minutes, waiting for the transmission to warm up. (My guess is there's a seal in there that doesn't fully hold until it expands.) Once it clicks in, the car is good for the day, as long as it's driven every few hours and that seal doesn't fully contract. She's on vacation and left the car in my care, so I've now experienced the phenomenon for myself.

After some dismissive crap from a local mechanic ("it's from 1985, just junk it,") I had her take it to my guy - he specializes in diesels, particularly old Mercedes, but has worked on some Volvos, too. He did a transmission flush (which helped make the transmission smoother once it's shifting out of 2nd), but recommended a rebuild to fully solve the other problems.

I've read here that replacing is recommended over rebuilding, as it's cheaper. So here are my two questions:
a) What kind of transmission is needed for the diesel model? I saw one on everdrive for $1099 that was labeled as a D24T, ZF22. It *does* come with a three year warranty, but that still seems kind of steep without installation.
b) Does anyone have any suggestions about how to handle the car until the new transmission goes in? My mechanic didn't seem to think that driving it was hurting it any further, as long as the rev count didn't get too high.

Thanks!