Your 400E would be the 124 model, I pressume.
124 models don't have very heavy pedals compared to the earlier 123 or 126 up to 1990.
Lubing would defintely help.
Reading this thread, I'm reminded of an auto journalist who complained that the testers in MB wears very heavy boots, whereas the Audi testers drive barefooted.
126 tailed by a 203, 129 leading the pack.