I had a problem with my '84 190e not cranking with a full battery and everything operational. I dont know exactly what was wrong with it but u cleared it up by removing and replacing the relays in the fuse box and the ones not in the box. I didnt replace them with new ones just put the old ones back in. after i got home i took each one out and put a small dab of dielectric grease on the contact posts to ensure that they were getting good contact then replaced it. this happened early this past summer so i dont really remember if there was a clunk sound on my car as you said that yours had. anyways its a cheap fix if it works for ya.