Have been detailing and tinkering under the hood of my '86 300SL for the past few days. When I removed the radiator last weekend I noticed a fine hairline crack on the upper (return) hose barb. Fast forward to this evening when examining further, I noticed on the inside of the barb a build-up of an hardened, dark colored, oil-type residew.

I can scrape it off with my fingernail, and it only is on the inside of the upper hose barb and extends down the inside of the tank for a very short distance. Doesn't smell like oil, but then it was soaked in collant. At first I thought it was the remnants of goo from a previous repair effort on the barb that are just breaking down.

This car has 66K original miles, and I've owned it for two years now. I have a very detailed maintence history with no mention of any such repair. Closest thing to it is a repair of a front oil cam (or distributor) seal, I forget which it is.

I recently changed the plugs (I believe the originals) and they looked fine. There's no whitish sludge under the oil cap or on the dipstick. The coolant I removed (was green...wrong type I know) was at least 3-4 years old, and had no signs of contamination. From what I can see with a flashlight and mirror, there's no signs of anything (crusty, oily, sludge or otherwise) on the inside of the radiator.

Can I do a leak down test on a cold engine? Seems it would be easy with a few ferncos and pipe fittings connected to the pump and neck fittings.

Does this engine (M103) have a history of gasket problems?

I'm hoping this is not a headgasket problem, but if it is I wouldn't be afraid to tackle it....or should I be?

Cliff