I've heard that geocachers have an eye for detail that allows them to see what other mere mortals overlook. While I believe this to be true it's always good to test one's hypothesis.
To find the 'final mystery' you will need to have solved and visited all 10 of the previous Diablobuster Mystery Caches. If you were paying attention, this final exam will be a breeze and FTF will be within your grasp.
If not, you may, (1) Attempt to solve the puzzle below using your geomath skills, or, (2) revisit the caches that you failed to commit to memory and try again. The choice is up to you. Good luck cachers.
0 (Zero Mystery) GC3J8QZ
1 (One Mystery) GC3J8TH
2 (Two Mystery) GC3J1FN
3 (Three Mystery) GC3JGQG
4 (Four Mystery) GC3JXKH
5 (Five Mystery) GC3JXMX
6 (Six Mystery) GC3JXMD
7 (Seven Mystery) GC3JGVZ
8 (Eight Mystery) GC3JXMM
9 (Nine Mystery) GC3JXM2
So who is FTF here? bassocantor? dprovan? or/and dprovan? basocantor? You are FTF, congratulations 
You can validate your puzzle solution with certitude.