Unscrewing the shroud from the trunnion can be a bitch as well. The problem at that end isn't from carbon buildup, but may be from solder. Some of the shrouds have been soldered on along with having that small locking screw. If soldering is suspected, just apply heat as you try screwing it off then once off, use a wire brush to scrub any remnants of solder away.
" The world is a very dangerous place, not because of those who do evil, but because of those who do nothing about them." - Albert Einstein, 1879-1955