I went to my favorite MB indy a few years ago and asked him about the glow plug issue. I had just purchsed a set of Autolites that were not working two months later.
He had Beru and Bosch, said he would give me the Beru. They were no better than the Autolites. Said if you need them take them, but be prepared to change them out again in a little while.
Went with the Bosch.