my sl500 started having a low droning noise at about 1000 rpm. unlike my old straight six sl the motor mounts are hard to see unless you go under the car and look. I found an easier way to check the mounts before they get really bad. open hood so you can see the engine, start engine, put in drive with left foot on brake, rev. if the left side raises that mount is bad. put in reverse to check the right mount. both side should hardly move. I found my left bad and my right ok. the left takes the most torque. After researching I found that oem mounts only last around 35k and should last 100k. so I found a couple aftermarket mounts from bilstein and febi through one of our sponsors (Pelican Parts) at a good price and at $99 for the 2, it includes shipping.

 

only took 18 hrs for me to replace the drivers side. left this old fart sore after crawling around on a cold concrete floor on my back. what a pain. yeah, the book says 8 hrs for both. I guess I need a bit more practice. most everything I said was a misdiagnosis. While the engine did lift about a half an inch on left and the right side hardly moved on the initial test, there was no loss of fluid in the old mount and the replacing did seem to help slightly in the vibration through the steering wheel and noise, it wasn't collapsed, so helping maybe wishful thinking. looks like I wasted a bunch time for nothin'. will replace 220 327 02 15 pulsation damper next for the noise. newer models have it on the pump, mine is behind the left wheel well. like on my r129, I'm going to have some extra parts.

 

it was the pulsation damper that was the cause of the droning noise, like a bad motor mount. life is good again. I have to take back my harsh opinion of oem motor mounts too.