This would not be a motor mount issue. What you are describing seems to be an issue with the transmission. IIRC, the C230 is a rear wheel drive vehicle. Only a front wheel drive vehicle would produce anything like what you are talking about with bad motor mounts, but then it will be far less noticeable. A motor mount problem will not create the jolt like what you are talking about, but rather a thump when releasing the gas pedal (relieving torque from the engine), plus you'll get a lot of harsh vibration during operation. Even with a broke motor mount, you'll still get power to the ground.
Other than visually inspecting the motor mounts, the only way I am aware of to test a motor mount is to power brake the vehicle. What I mean is, while you are sitting in the driver's seat, apply the brakes tightly, put the vehicle into drive, and start applying power. While you are doing this, a second person is needed to view the engine (so you must have the hood open). What the second person is looking for is if the engine lifts off of its mount. It would be a definite movement and not just a slight torque over (I'm talking inch(es), not millimeters of movement). You'd also need to do the same thing in reverse to check the other side. Usually, the side which lifts when in drive will be affected far earlier than the other side as it takes a lot more abuse. You can utilize the parking brake on top of normal braking to perform this test. Please be careful in your surroundings. Do this in a place where, if the brake should slip, you won't run into anything. Ensure your assistant is off to the side of the vehicle and not in front of it.