You should realize that the vast majority of KB's are caused by faulty (over-pressure) ammo, or barrel obstructions. Yes, there are examples of KB's being caused by manufacturing errors in modern rifles - witness recent Sako barrel faults.
The M98 is a stronger action than the M96 - they are referred to as large ring vs small ring. Also, the M98, being newer has several design refinements. However, the wild card here is the possibility of a given rifle having slight metallurgical flaws in certain critical areas. The flaw propagates over time, until....
75 years ago, they did not have examination techniques such as radiography to survey for flaws - they used proof loads. This method is quite good, but not perfect. Additionally, factories developed reputations for providing quality steel. Both the Swedes and the Germans enjoyed this reputation early in the century. I'm not sure you could make the same statement about production in war torn Central Europe during WW2.
So, if your contemplating purchasing a 75 year old M96 or M98 rifle, you can be reasonably assured that it left the factory as a reliable firearm. However, after 75 years of use, part changes etc., that may not be the case. If you want to be certain about the integrity you may consider having the rifle checked over by a competent gunsmith, and possibly radiographed in critical areas.
