More thoughts
I did not realize my first K98 had a duffle cut until I went out to shoot it and noticed the end kept working its way off when I shot it. I was disappointed in this. I was only a teenager when I got it (1980's) and had not even read any literature on collecting K98's. I also did not even realize I was getting a "bolt mismatch" at the time. I now realize that the rifle is a vet bring-back, bolt mismatch in good shape. It is a 1938 S/27. It also has a "O" number on the disk, apparently a navy mark. I also think the stock may be lightly sanded. Anyway, back to the duffle cut--when I shot it, I noticed that someone had put a piece of folded sheet brass next to the barrell to wedge the piece in to help hole it on. I did nothing to the rifle for years. Later, my dad and I aqcuired a few more K98's. My dad got a duffle cut one that was all matching except the band spring, which was missing because of the duffle cut--the whole front piece was so loose; it just kept coming off. With these experinces, I looked onto the internet a few years back and learned about duffle cuts and was under the belief that a good repair was acceptable. Anyway, my dad and I thought a repair to both of ours would be an improvement. So we did it in a similar way as Hambone (I may have read of his method several years ago). We used wood dowels instead of threaded rods. We also made the holes a little larger than the rods so that we could line up the pieces perfectly. We used small peices of wood for spacers to compensate for the saw kerf. We then used epoxy and only glued the pins in with a little extra to hold the spacers in too. To let it dry, we put the guns back together with some wax paper to keep the metal from being glued on. This allowed the wood to be perfectly aligned (or at least we think it did). The next day my dad took the guns apart and finished the job (I live out of town and did not stay over long enough to finish it). We had saved the saw dust when drilling the dowell holes and my dad mixed it in with some more epoxy and filled the gap in the cut while the stock was off the gun. The next day he put the guns together. They have been together ever since. He said the repairs were good. The guns have not been shot or even taken apart since then.
With all of that said, I still have some mixed feelings about the repairs. Part of me says it was right--they can be shot now without the ends coming off (hopefully) and the pieces will never come off and get lost just by handling. On the other hand, I can see how it is best to leave things alone. Also, my dad's gun is probably very valuable--it is all matching 42 code 1939, solid wood (not laminate) stock, sharp markings, excellent condition, with an "L" on the stock. Of course, the band spring is no longer matching; it has been replaced with an unnumbered one (I think my dad had to try two or three before he found one that fit well).
As a collector, I think we have to accept the facts: A duffle cut makes the gun not "as issued" or even "as used" by the germans. It is clearly an alteration. Timing does not matter that much--If it was drilled for a scope by a GI, that would ruin it, even if done the day it was captured, I believe. I definitely prefer vet bring backs, but if I saw two similar rifles for sale, one duffle cut, and one uncut, I would probably get the uncut for the same money. I would was also probably get a repaired duffle cut over an unrepaired duffle cut with loose parts that want to fall apart. Lastly, I saw a pawn-shop k98 for sale awhile back that was in good shape with this problem--it was duffle cut and in pieces, with some lost gone, including the the entire top piece of the stock. So, at least in my experience, duffle cuts will lead to lost parts.
With all of that said, I hesitatingly come down on the side of making the repair--I don't think you loose any value, you make the gun more shootable, and lastly, no matter what may happen to me in the future, I can assume that even in the hands of a careless person, the rifle will at least stay together.