Completed SB-00053. This service bulletin included inspection of the lower tailcone skin for cracks adjacent to bulkheads and installion of new tailcone stiffener clips to prevent future cracks from developing. If cracks were identified, an external patch was to be installed as well. Crawling, sliding and wiggling into the tailcone was no small feat, and much dreaded. However, once pads were fabricated and placed in the tailcone and external rivets drilled out, it only took 1.5 hours to crawl inside, remove necessary internal bulkhead rivets, install the clips and vacuum up any metal/rivet debris. Fortunately, no cracks were found, so external patches were not needed. Still, something I'd rather not do again! I also took advantage of access to the tailcone to replace the ADHARS unit, per updated SB-00028.