Another easy check is to pull the plugs and compare.

A cylinder that is seeing water will often have a very clean looking plug relative to a used one that is not seeing water.

Remember the trick about slowly pouring some water down the carb throat to clean carbon off the piston and valves?

Jim

__________________
14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles