Have a 91 500sl has symptoms of crank position sensor failure .

Hey I have the same problem # Hi I have a 1991 sl 500 I got it from my dad after my 2nd deployment to Afghanistan and i was very excited about it but I start having problems with it . # when I drive it for 45 minutes and it gets hot the car won't accelerate any more and it don't move at all , but when u park it and it cools down its good to go , I took it to Mercedes dealership and they said it might be the ignition module but they weren't sure and they said just the part cost 3500$ just wanna know what could he the problem