Manual Engine Oil Check for C-320 is possible. While I love electronic gadgets (Mercedes engine sensor), there’s nothing better than the old lay-your-eye on the mark. Before I share the Mercedes secret, I digress for a moment. Mercedes is the really forthcoming in this information. I say this because it took buying a $160 repair CD manual and going to 5 different service shops to get the truth. Although the manual provided instruction on manually checking engine oil, the first 4 service shops basically called the manual a lie. Then the one service manager told the truth and sold me measuring tool (W-140-589-15-21-00) for my C-320, 2004 model. Now the solution: there’s an engine dipstick guide tube that is located on the passenger side at the rear of the engine, next to the transmission dipstick guide tube. You must remove the air filter to gain access and the cap has a locking pin that you must break to remove. Once removed, than use the measuring tool to manually check the oil level. You may also use a vacuum pumping tool to remove the oil, instead of removing from the engine bottom. The tool can also be used to check the transmission oil level as well.