My dad (many years ago) purchased an imported W124 230E and the same thing happened to him while driving in town one fine day. The same symptoms and embarassment. They found the fault to be the OVP relay and the unit was located near the battery console. Some cars, as he was made to understand, has the relay located in the glovebox compartment.
Since the replacement, he never had any probems with it.
This all happened while I was in Australia so I didn't get to see it all first hand.
Hope this provides the solution for you.