I don't have the diagram, but the guide I've used (taken from a thread somewhere on here) is:
Starting at the front: The small box sections in the front panel where the subframe mounts are, accessed through the access hole in the front panel.
Bonnet stiffeners, particularly the front ends, accesses through various holes in them.
Scuttle corner box sections, access from engine compartment, there is a gap between scuttle & inner wing.
A-posts, access via hole where door check bracket operates.
Sills, either drill a hole in each section fore & aft of the jacking point & fit grommets afterwards, or insert lance via the sill flutes
Seat mounting box section, access through holes already there.
Doors, remove pockets, if fitted & release bottom of door card.
B-posts, there is a black plastic cover, facing the rear of the car which can be removed & you can spray into there.
Side-bins & rear sill sections, remove trim from sidebins & spray waxoyl liberally into the rear heelboard end & down the side panel, There is also a sill box section in there & with a waxoyl extension probe, you can get to that from the hole drilled in the sill section behind the jacking point.
Rear wheel arches, not exactly a box section but it's important to allow waxoyl to run all around the inside where the arch meets the side panel.
Inside boot, small box sections where rear bulkhead, boot floor & wheel arch all meet, access through holes already there.
Boxed ends of rear valance, if it's original & 1980-on you can access the right hand one through a hole in the corner of the boot floor where the rear fog light wires run. Left hand, remove grommet beneath bumper which covers the hole for a second rear fog mounting.
Stiffeners in bootlid, via gaps between stiffener & skin, put plenty at the bottom of this.