Greetings! New member here. I'm quite experienced in automotive repair and restoration, but this is my first endeavor in the realm of Spitfires. I have a couple of questions regarding the rear bushings on my '78 Spit differential housing. I purchased new replacements for the car, but my existing bushings seem exceptionally firm and solid with no signs of dry cracking andminimal surface rust in the sleeve hole. I would like advice regarding simply reusing the existing pieces versus installing the new. I also have tapped the bottom of the housing and installed a drain plug to facilitate simple lube changes in the future. My car has the fibre shims behind the planetary side gears and they were missing. I have purchased new fibre replacements as the brass versions are not to be found. Any advice regarding these questions would be greatly appreciated!