I never noticed the maintenance free disclaimer in the manual of my 98 E300. It definately has the same battery - big white Mercedes Benz group 49, philips head screw caps and all. Maybe that same battery wasn't maintenance free in 1998

Anyways, I added distilled water to it for years. No problem. It just died last week, so it lasted 5.5 years - not bad. I replaced it with an Optima orange top - fits great, spins that diesel like it's a toy engine.