I guess I am wrong. I thought the improved vac pump was introduced with the late W123s.

Regardless, I don't think there is engine damage ... yet. So long as the engine is still running relatively smoothly and without expensive-sounding noise, a loss of power does not indicate serious damage.

I had a similar failure on an old W116. I had it flatbedded to a shop and they inspected for damage and replaced the vac pump with no aftereffects.