1. OM616.912 engine from 02/76 to 02/79 have 65 horsepower;
from 02/79 to 11/85 have 72 horsepower
2. The automatic and standard transmission 240D's have the same horsepower output. However, with an automatic transmission, the 240 is as lazy as an ol' coon dog on a September afternoon. It just doesn't move. The perfect automobile for a teenage daughter . . . safe and slow. If you really don't care what time you get there, and don't like manual shifting, an automatic would be fine. If you want to experience the thrill of controlling your motor, the stick is the way to go. When I had my transmission pulled for something or other at 250,000 miles, the mechanic couldn't believe the condition of the clutch. He said it was like brand new. A stick shift also saves brakes. I finally put the second set of front brake pads on my stick shift Ranger at 210,000 miles. Only had to put one set of pads on my 240D in the 200,000+ miles I had it.
A useful site for W123 owners:
http://www.geocities.com/SiliconValley/Pines/6633/w123.html
Kinda spartan but some good tech info available.