Our 2-valves Boxer know two types of starters, the Bosch DF 12V, which became somewhat more powerful with the release of the /7 series, and the Valeo D6RA-15, which was used from the mid-1980s onwards. The D6RA-32 is also supposed to fit 1:1. On the left a BMW K series starter, the BMW R series starter on the right.
You can roughly characterize them like this: Bosch: Large, heavy, high power consumption, low susceptibility to interference. Until model year 75 (production Sep. 74) the pinion has 8 teeth, after that 9 (also the flywheel was changed).If you give it a simple general overhaul after every 100,000 km or 20 years, it will last at least as long as the rest.
Valeo: Small, light, torquey due to planetary gears, less power consumption, occasionally fails due to fallen magnets. The most common Valeo is identical to the Bosch from 75 up; for replacement needs, a type with 8 pinion was also introduced for the older models.
Around 2002, production was moved to Poland. The starters produced there are less durable than those of Valeo France. Very special caution is required with the cheap clones from the Far East; here housing bells break early.
The Bosch starter can be easily disassembled, cleaned and overhauled with basic knowledge of mechanical engineering and a few common tools. The Valeo can also be overhauled, but if the mentioned magnets are broken, a replacement of the housing is necessary.