For those of you who may need to get the injector pump off of and back onto a 4.108:
A ball-end hex wrench will likely save your sanity. The inner bolt is the one that is the RPITA, and unlike the outer two hex head it's a socket head screw. Double check which size to get -- the bolt itself is 5/16" UNF. My screw takes a 7/32" hex key, but most 5/16" socket headed screws take a 1/4" hex key.