Ok, just done my first oil change on my 2002 slk 230. When I removed the old oil filter, the filter bowl was still 3/4 full of oil. This took a good 30-40 minutes to drain out!! Is this normal? I have never done an oil change on a car using this type of filter, all my previous cars have had the metal canister type. I was just a little concerned about the very long drain time. And yes, the engine was hot.