Someone, in another message, wrote: "...I have the black top relay and I want to replace with the red top one which I hope to order from parts shop..."

So, what's the difference between the red and black-top versions of the relay, and why would someone WANT to replace one with the other?

I wrote that message. There are a few DIY updated and redesigned parts on early model W124's and 190E's. Mine is an 88. The radiater cap (now 140 bar), the thermostat housing (now metal I believe, mine is still plastic), OVP relay, e.t.c. I change my stuff just for peace of mind, I don't think there is any need to change yours unless you suspect a problem or are doing an overhaul of certain systems.