I have an older Kieffer Wein DL Professional that has served me well and been a good fit for almost every OTTB I've had. Except the current one, which needs a slightly wider tree. Do I remember correctly that someone or other can widen a Kieffer tree? I have a vague memory that they are like Prestige saddles in this regard, but need more info and a pointer toward who can do such a thing.
I had 2 Kieffers on trial from Pelham Saddlery a couple of weeks ago. I asked them about the process. They told me that the trees can be adjusted, but not an unlimited number of times. This is done by a process similar to the one used for Prestige saddles. In fact I was told the Prestige equipment can be used on Kieffers and is easier to come across than the Kieffer equipment. But you'd probably need to verify that with whoever does the work.
Patty Barnett at East Crow Saddlery in CT (email@example.com) can adjust the tree, and will do a wonderful job. As Bristol Bay mentioned, whomever does it will need the proper equipment (I believe the Kieffer trees need to be heated, since the trees are synthetic) and know-how. If the saddle is under warranty, be sure to use a Kieffer-certified shop to do the work, or your warranty may be void.
Thank you to all - I appreciate your responses. It is definitely not under warranty, but I wouldn't want to take a chance on having the job done poorly. The saddle has been great, and I would like it to go on being great in just a slightly wider way! I will contact Patty and also investigate other Kieffer-certified shops.