One disagreement with above; use green scotch brite "scrubbie" pad vs sandpaper to clean all sealing surfaces, it has a finer abrasive so will make for a smoother surface.

As others have noted, it's not difficult to pull the fan and shroud to get in to replace the thermostat or water pump, if you have an alternative car to drive when those parts fail, I would personally wait to replace them. If they appear to be original, I would maybe buy the thermostat to have on hand, I'd even keep it in the trunk next to the spare tire and bring a 1-1/4" wrench with me on long trips (to remove the fan): only "snug" the fan nut and you can remove with 1-1/4" wrench and a hammer.

__________________
2011 E70 • N55 (me)
2012 E70 • N63 (wife)