Mystery vibration at 25 mph can't be diagnosed. It's not the front end!

B&T joints are actually very easy to service once you know how to do it, providing the wear is in the rollers and not in the body itself.
One catch is that replacement boots are nearly completely extinct. Quick, cheap trick is to use a boot from an off-road style aftermarket shock absorber. Most 4x4 shops can hook you up with one.
Cut it to about 8 inches, and feed it through the inside of the B&T body before you assemble the joint