I try to amass as much as I can with regards to manuals, CDs...and this forum. You are right. Some instructions are too vague or just aren't there at all. SO you have to try other means.
Then there is the just-go-at-it-and-see-what-you-can-find method, making you either a subject matter expert, or the goof who just destroyed a perfectly good (and expensive) part. I usually fit the latter description ...
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