Hi thanks for the question, problems like this can be as hard to diagnose as they are to live with. It sounds like you may have some intermittent electrical issue. This will require a skilled technician that has the knowhow...
The tumblers are part of the ignition switch assembly on these vehicles. This part must be replaced as a unit. This particular part malfunctioning is a common problem on late 1990's Mercedes Benz products. Have a mechanic who is familiar...
If the key wont turn normally try to jerk the steering wheel side to side while turning the key. If this does not free up the ignition then the ignition switch is likely the cause. When tumblers inside the ignition...
A Check Engine Light could mean hundreds of different things. The first thing I would recommend is to have a qualified professional inspect the Check Engine Light (https://www.yourmechanic.com/services/check-engine-light-is-on-inspection), they will use an OBD2 code reader to find which code has...