Funny one (interesting - W126 560 SEL)
 

I am about to do the water pump, while I am also doing the plenum seals. I pulled off the top housing off the water pump, the one that has the hose from the top of the radiator and also the hose going into the intake manifold.

Since I have the parts pulled, I decided to clean up that housing. As I soaked it and then rinsed it, a piece of rubber type gasket compound came off.

What?

This part has never been renewed, it is original. It seems that they felt the paper gasket was not enough of a seal, and added some gasket-maker to this mix. Not a thing mentioned in the manual of using a suitable gasket making compound, yet at the factory they obviously did.

What do you make of that???

Are you a one owner, and have done all repairs on the vehicle?

Nope...
 

And I suspect you are tight... Somebody might have futzed with it before....

But why? The car had 97,000 miles on it when I bought it, and I am the third owner.

Maybe the 97K could be in question also.

At 30 years old someone may have replaced the thermostat or the original gasket deteriorated. Many times sealer is used to compensate for rough / warped surfaces.