Originally Posted by pfbenz

I didn't know the 123 blowers changed over the model run. I thought that a blower from a later 300d would fit in an earlier 240d. I'm assuming your your 240d has air conditioning and has the blower mounted on the passenger side, more or less under the glove box. Are you sure a later 123 blower won't fit?
If by chance you have a 123 without factory AC, with the blower up under the dash on the passenger side of the console, you can find a blower motor for a small pickup that you can get to fit, I used to have a euro 300d with no AC,and I threw a blower from a late 90s Toyota PU in it, the mounting flange was just a slightly smaller radius on the Toyota blower, but I was able to fit it with slightly longer screws.
In my 1982 240d, I currently have a blower I believe came out of a 116 chassis Benz, only 2 of three mounting screws fit, but it stays up there. The Benz blowers on the models with AC are different from other squirrel cage motors I've seen because of the way the motor is recessed inside the squirrel cage so it doesn't intrude into the passenger side footwell space. I'd love to find one of similar design.
A "standard" squirrel cage heater blower motor might not extend all that far into the passenger footwell, but you wouldn't be able to mount the cover panel that fits under the dash.
I hate to throw this out there because of their terrible reputation for poor quality, but Google "URO 1238201642", I see that blower listed as fitting both my 82 and your 77 240d.
Everything I have ever bought from the URO corporation has been junk, but all I have bought from them have been motor mounts, suspension parts, and a 123 inside hood release, all junk.
But who knows, maybe URO is really good at making small 12 volt electric motors.