Altho somewhat less emphaticaly, i agree with Craig.
Nonetheless, if u plan to stay wityh the Bendix TV then my recommendation would be the Neatsfoot oil. Since u have it apart u mite first use saddle soap on the leather seal to get it good and clean before applying the neatsfoot oil.
DISCLAIMER: to some extent i hesitate to recommend the saddle soap because it is used in conjunction with water and this IS a brake system . But saddle soap followed by neatsfoot oil has proven over the years to be superb for my many m/c leather goods i have. Some got saddle soap followed by neatsfoot while others got only the neatsfoot oil. The jackets and mudflaps (yes GENUINE LEATHER) and other items are much better that got both than those that got only oil. Nearly all of these leather items are at least 25 years old and in some cases nearly 70 years old.
Usualy several applications are needed. Don't rush the job.
Just want to second the motion about Ed Strain's work. He has rebuilt two Treadlevacs for me and does quality work. His phone number is: (800) 266-1623