I have no experience with the W140's tranmission.

However, transmissions are usually rebuilt because their clutches or bands wear out and/or their valve bodies get contaminated and won't allow the springs and valves to move.

In your case, the transmission works flawlessly, most of the time. Every so often, given a specific set of circumstances, it fails to shift. Then, when shutdown and restarted, it performs flawlessly, yet again.

So, your problem is almost certainly one of control of the transmission via it's computer and/or various sensors. It's very unlikely that the internal components of the trans require a rebuild. If so, the "problems" would be apparent every time you drive it.