The Bosch pumps seem to be a bit beter for wear than the Hitachi model. Its hard to tell them apart. They look the same, but they are NOT.
I have three, two hitachi's and one bosch. Both hitachi's show signs of wear and one out was out of a 280zx with 76,000 km. The bosch has almost 180,000km but in remarkably good condition except for a leaking o-ring around the housing. Still trying to gather the courage to pry it open and change the o-ring. The motor section is none servicable.
If you do dismantle the pump, pay particular attention to the position and direction of the centre disc. The hole in the centre for the pump is offset about 2mm iirc. Changing position or flipping it over will effect performance.