Sorry we didn't pick up on it sooner
Sorry we didn't pick up on what you were saying sooner. We all, at least those of us with the 300E series automatically think broken radiator neck when you start talking leak in that area. I believe mine to still be the original in my '86 300E and still no hint of breakage. I actually think a lot of breakage occurs when folks use the neck as a leaning spot when removing the air cleaner housing. Seeing as I do my own maintenance, I understand that weak point and avoid using it for such purposes. I wouldn't change the core either, chances are if you take care it will most likely last another five or more years.
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan