100k BMW miles is like ...
I would say BMW's need far more servicing per mile than any American or Asian car (on average). For example: BMW's regularly wear out their front suspension parts in about 50kmiles. So, at 100kmiles, if the control arms and steering rods are not new, they'll need renewing soon to retain the original/new handling. Figure $2500.
At 100kmiles, it would not be unreasonable to think the shocks will need replacing soon ($1000 parts plus $500 labor and an alignment).
I would not buy a used 5 series without a long extended warranty.