DDK - Die Deutschen Klassiker

Bruce Andersen's Performance Handbook is also a great read.

The starter dog is not throwing properly. Its not your battery. There is a solenoid that is sticking. Put the car in second gear, take the handbrake off and rock the car back and fourth and that can often release the sticking. Faining that you should hit the starter with a wooded mallet to free it up.

Its basically a sprung steel two pronged retaining clip. Spray some wd40 on it and then pull the clip with brackets. All the dirt and brake dust gets in there so it makes it hard to get off. Just yank it and it will come free. I just did the same to mine.