I have an 86 635 with auto transmission. When at speed it will drop out of gear into nuetral. I simply go from drive to nuetral and it kicks back in with no trouble. This happens rarely (never when I take it to the shop!), but its becoming more and more common. I've had it serviced at a good shop, but since it runs perfectly for them they don't know what to do. Any ideas of what may be the problem?? Thanks in advance for any help...