If the blade moves and oscillates, then all you need to replace is the motor. It's a tedious job, but not impossible. If the blade doesn't oscillate, you'll have to disassemble to determine the problem. If the gear is broken, these are available as replacements if you need one:

https://www.odometergears.com/products/Mercedes-Benz/E+class+%28124%29++84-95+Mech./50