I have a manual transmission 97 BMW 540i. It only starts normally if I drive it frequently. The more frequent I drive it, the more chances it has at starting up. If I leave it too long, it will be basically silent - no telltale battery low sounds on startup. I do hear some kind of servo type noise. If I try maybe 50X plus, it may start up randomly if I am lucky - the less time that has elapsed since last startup will increase my chances of the car starting. In this state if I hook it up to a battery to jump it, it does not change the behavior - same no start. All the cabin lights and accessories are strong and does not seem to be a battery issue. I am able to get the car pushed and can pop the clutch and the car will start.
I had the starter replaced about 6 months ago with the same problem and it seemed to fix the problem until recently and it is showing the symptoms above.
Could it be the starter again? or is it only a temporary fix for a different problem?
If I drive it very frequently - absolutely no issues - starts up immediately.