I have a technique that no one else seems to use. Basically, I'm using Scotch-brand Hi-Strength adhesive in an aerosol can (No. 90).
I mask and spray the body and the leather, wait about a minute and the press the two together. It's a rather permanent bond, so keep that in mind. You only have about a minute to work the leather before it sets.
There also is a No. 77 adhesive, but I find it to be only medium strength.
My latest project: Zeiss bumps on the back and major bumps and corrosion on the front. Stripped off the leather, cleaned the body, painted the brass rivets black and rebonded and then treated the leather.