The Penetration Testers Open Source Toolkit vol. 2
and NIST SP800-42 (it's outdated I know, but read it anyway. It will give you some good ideas you can use when you perform pentests.)
Also, about privilege escalation:
- On Windows, the Meterpreter shell has a lot of options including privilege escalation, is it not possible to use that only? (Code your own exploits, and use a meterpreter as a payload.)
- On Linux, did you search on Exploit-DB for privilege escalation exploits and checked what was running on the target machine as root with "ps faux"?
It's just a few ideas, to help you the next time you attempt OSCP because I actually believed you would pass

For now I would say that you could (or should) play with similar challenges and prepare for your last and final retake (where you will certainly pass).
Nothing is impossible, it just takes time!

Anyway, good luck with whatever you choose to do now. I'm sure you will pass OSCP the next time if you study hard for a long time and prepare yourself even more, remember, expect the unexpected. Especially during OffSec exam challenges ;-)
Best regards,
MaXe






Something for people already knowing Web App Sec 
Network Pen Testing : AIX Vulnerability Assessments




