Yes, it was a little bit hard, first you have to cross-loosen the bolts of the front differential axle to get access to the ISM, the problem is that there is enough room for a impact screwdriver.
After removing the bolts, you can push the axle to the front and now you have to loosen the 4 torx bolts of the heat deflector, again, you will need a small tool to get access to the upper bolts.
Finally, the easiest part, you have remove the harness conector, the 4 bolts that holds the ISM and the vacuum hose.
After replacing the ISM, the hardest part is that the bolts of the differential axle must be cross-torqued first with 20Nm and finally, 90 degrees. I suggest you have someone stepping the brake of the car to do this torque.
Best regards,
Sergio

Hey How did you replace your ISM on your GL500. Was it hard?

Thanks
Tek