W113 280sl coolant tank cracked

[my6.3]

Has anyone else seen a coolant tank crack open on a w113? This is a low mileage garage queen car. the metal coolant tank has spit open on the top..I've never seen this before.

[my6.3]

I forgot to mention this is a brass tank. it split open on the top side away from the seems,near the cap.. like a tuna fish can. I question was there stress in the metal from the fabrication? I've never seen anything like this...just curious if anyone else has.It's thin brass, i guess it could fatigue over time..just odd though. The car has <15000 miles.