What is this part on an 87 300e?
 

The past week or so, I've noticed a smell that I believe was coolant leaking onto the headers. This morning I saw a coolant leak coming from the housing of a (watercock?) valve right by the headers. I've been using the heater a lot recently here in Virginia, and I just bought this car from my sister in Miami (she NEVER would need to use the heater), so I assume that this part crapped out from years of disuse (seals cracked, whatever). This looks like it would be an extremely simple fix...but until I get my shop manuals, can someone please tell me what exactly it is? the pump/motor looks fine, the black housing (circled in green) is slowly leaking as if a seal is busted (the second picture shows this better). Thanks for your help!!!

On my 260E 1988, it is the auxillairy pump for the cabin heating, should be the same on yours.

That is correct, the pump keeps water circulating at idle to provide appropriate heat to the cabin. Do a search and you will find some have repaired the seals on the pump. I had a similar problem and took the easy route and replaced the pump.

I tried to repair the one on my car, without success, finally it ended with new pump 200 euros).

Should I disconnect the electrical...
 

until I get it replaced, or will it continue to leak through the housing and possibly seize the pump's motor?

One option is to remove the pump and connect the input/output hoses with an elbow used for plumbing. I have a new spare pump, let me know if you are interested.

Watch out, too, that the pump doesn't seize and short out your ACC control panel.

Get another non leaking pump as suggested above - or else you could end up spending more money, as suggested above.

I know I am pretty much repeating myself...but I wanted to post just in case you missed the urgency of getting it replaced. (a good, tested junk yard unit will do - one that doesn't draw too many amps -- Sorry, I don't remember the amp draw threshold)

Thanks
 

I'm disconnecting the electrical connection until I replace the pump. When I do replace the pump, any tips on preventing the loss of too much coolant? Also, how would I go about "burping" the system after I repalce the pump and add more coolant. My old 300zx had a radiator cap at the top of the cooling sytem making it an easy job. Thanks for your advice and input!

depending on the condition of the hoses, you could try to pinch a section of hose on either side of the motor with forcep-like pliers to stop the flow of coolant when you remove the motor. you will still introduce a small amount of air in the line when you do the swap, but the system will be able to purge that out by itself automatically after a little use. considering the age of the hoses, you'll have to be careful not to damage them when you 'pinch' them. In fact, what you might even consider is getting a helper to pinch one side by squeezing the line hard with just his/her fingers while you disconnect the fitting on the motor assembly. When the hose is off (their still pinching it somewhere a few inches away), you could quickly plug the open end of the line with some kind of stopper, like a cork. Repeat process on other side, take out old motor, get new motor, reverse process. You'll lose a little coolant, but if you're fast enough, the amount of air you'll introduce to the system will again be minimal enough that it will purge itself after restart.