The head on my low mileage '91 300E was removed, checked and found to have no problems. The head gasket leaked despite annual MB/distilled water coolant changes, Mobil 1 since the 1,200 mile mark and never any overheating. This engine never had tap water in it until the dealer used it to flush out the oil in the cooling system.

I'm not suggesting that the head shouldn't be checked but it doesn't take much to have a head gasket leak on the M103 and I'll bet most of the time the head isn't warped.