you need to find out if it has nikoseal liners
its a common problem on the nikoseal linered bores
its sumfin to do with cracking
bmw changed the material it was made from because it was a known problem

i may have that the wrong way round, it may be that they changed it TO nikoseal liners to fix the problem, i'm not 100% sure
but i think its the way i said it 1st time