I came across a couple websites lately that I found useful, so I figured I'd share. I assume you guys have lots more, so this thread can be a catch all reference if you want:
BMW Technical Information (most models):
https://www.newtis.info/
Auto Maker Mktg Brochures (PDF):
http://www.auto-brochures.com/index.html
Porsche Vin Decoder:
https://vinanalytics.com/
BMW Vin Decoder:
https://www.mdecoder.com/
A site that searches private for sale listings at multiple forums:
https://hiddenrides.com/