On the definitions of repair versus maintenance:
Repair is pretty simple to define...replacing one or more broken components is definitive of a "repair".
Defining maintenance is hazy at best, but typically, maintenance involves "adjustment", not "replacement" of tangible components. What makes this definition hazy, is that you have to exclude "fluid" and WORN parts as "tangible" components.
If, during a typical maintenance routine, one discovers a "tangible" component that has failed or is at the point of failure, then the "maintenance" switches to a "repair".
What makes the definition hazy, is that there are different views of what "non-tangible" components constitute maintenance.
Most of us can determine this by looking at what manufacturers cover in a basic powertrain warranty. Although, MBs are pretty reliable beyond 100K, the powertrain list was probably developed early on looking at statistics of a typical ownership lifecycle, which ended at on or less than 100K. During that period, anything that was found to "wear out" before that period, was considered a "wear" item, and thus fell under the "maintenance" category.
If for example, piston rings would wear down every 20K miles or so (but of course, engines would have been engineered to make that repair as easy as changing oil), doing a ring job would be considered "maintenance".
That said, maintenance includes replacement of tangible parts that fall under the "wear" category.
To add to this confusion, if a part that falls under the "wear" category fails prematurely (or what the manufacturer considers premature), then it is a repair. Replacing worn tires is "maintenance"...replacing a prematurely worn or blown tire is a "repair".
Labor intensity is not a factor. Timing belts, while time consuming to replace, fall under the "wear" category under most powertrain warranties (thank God MB doesn't use them). Therefore, replacing a broken timing belt is a repair...replacing a WORN timing belt is considered "maintenance".
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car