There are several opinions asto why they are more expensive, But here is my take. While they are stamped with the same bore desginations as their new counterparts, the prewar bocals were made with a different bore, wall thickness and metal alloy formulation. They in essence cannot be made anymore because the master mandrel, and the metal they were made of no longer can be made. While no 2 bocals play exactly the same their is enough consistency in their playing characteristics to know they are indeed different. Part of the reason why they are much more expensive is that prewar bocals that havent not been physically damaged, modified, or altered, are not getting easier to find. Alot of them have been kinked, bent, heavily dented or very commonly have had the seam split on them due to how thin the metal is and thatthe solder seam can degrade and weaken. Alot of times they can be repaired but bocals are sensitive to certain changes and resoldering a seam can cause the bocal to play differently. But the dwindling numbers of good examples and demand are the 2 prime reasons.
By now your probably asking "Do they really play that good?" The question of whether their good or bad for you is a very subjective issue. For bassoonists that play instruments based on prewar Heckel designs they can compliment the bore better and help alleviate some tuning issues. I found on my own instrument (8200 series Heckel) a prewar bocal that matches the instrument appropriately allowed me to use much lighter darker reeds, and really helped with alot of intonation quirks. I have several customers and colleagues that play similar instruments, and they found much better success with modern Heckel bocals as well as other brands of bocals. It totally depends on your instrument and reeds, and concept of sound. The only way youll know is to try them.
Hope that helps, Good luck in your search for the ideal bocal.
All My Best,
Taylor Bassoon Services
723 Steamboat Ct
Ottawa, IL 61350