Don't know why your gear wrench wouldn't fit. This is the one I used with 4 sizes, 13 being the biggest. I have also used a flex head 13 mm gear wrench which also fits but this one, being non flex was used to break loose the bolt with a pipe and mallet. The screwdriver was used as a wedge and kept the wrench from falling off. I can see taking an hour or more if you use a box end bent wrench.
wrench on the end bolt. Oil cooler line did have have to be removed.
Pipe resting on the wrench
