So here is a story that would probably get me stoned over in Rick's Facebook group ... But maybe somebody here will find it useful.
I bought these two used XM-18s over time, one Skinner Krein Regrind (posted pics of the knife before), and one Vintage Bowie. After using the Bowie for a while and comparing it to my backup, I noticed that the blade was a quarter inch too short. Guessing the original owner broke the tip, it was reground and he failed to mention it on ebay. The Krein Skinner (early Gen4) was well used, with a great blade, but shot lock-side: detent ball mostly flat/gone, 70% lockup, and lock-stick that I couldn't get rid off (usually, my XMs with stick wear in nicely).
So I swapped the Krein blade into the Vintage and it came out very nice. This kind of swap probably doesn't always work, but in this case it did. If you try on your own knives, you need to swap the stop pin too, as it affects the detent (they are of different thickness across different XM-18s), and you might need to swap the female side of the pivot, too, depending on how the blade fits.
Cheers,
Roland.