He's never said it was uber reliable, the guy only just got the thing, although the E39 is known to be reliable relative to the competition, i think sepending the £500 or whatever is the way to go, its what i've spent in the past on my 318i in one go when a few things needed doing and at that time only covered about 90K,
The 530i sports retailed £35K + back in the day, so big bills are going to come sooner or later, thats the used car market, as long as your not paying too much over the life of the car, can afford it and get driving pleasure from it who cares.