Well i had to rebuild mine at 150,000 km's becaue the rings and pistons were worn to shit and that damn lucas film crap was gumming up all the oil passages with gunk!
Never found the reason for the hard starts.. but after it was rebuilt it started like a dream.. no smoke, no studder... nothing. It fired up better then ever. hard starts are usually a sign of bad compression and bad ignition.
But if you motor has that many km's on it i would consider replacing it with an M20 or M50
The major difference between my 318is and an e30 M3 is that the noises come from the engine and not the passengers