[PeteB1]

I've always thought of the process of moving from 'N' to 'D' (and back) in an automatic with clutch/brake bands when stationary as being similar to the manual engagement/release of the clutch in a manual when stationary except it is done through servo's and hydraulics . Each time it is performed, there is some wear on the bands so the more often it is performed, the more accumulated wear over many thousands of miles. Replacement of the bands when sufficiently worn to require it is obviously a major operation. Therefore, even if the oil does deteriorate faster if regular and frequent stop/start driving is done without leaving 'D', it is cheaper/easier to replace as and when necessary.

However, my analogy with a manual clutch and my idea of what causes autobox component wear could be completely wrong so I may be unwittingly doing more damage by keeping mine in 'D'.

I'm not sure what happens though in a modern automatic fitted with auto engine switch off when stationary/restart when ready to move again as this would also necessitate 'D' to 'N' switching and back.