The manual does indeed discuss adjusting the doors. If you don't have a current login to the online manual, email the factory (or me) and you can get a logon to check it out.
In general, since your car has been built for a long time, presumably the hinges have just come out of adjustment. It's pretty common.
One way to address this is first make sure all the hinges are securely mounted to the body (both the top and bottom), then remove all the panels in the way of adjusting the bolts from the hinges to the door. With a friend on the outside making sure the gaps are still correct, then tighten or loosen the nuts on the lower hinges. Open and shut the door carefully, and adjust further as needed. Adjust the top hinge as needed, but this doesn't move much unless it has drifted under the fiberglass- and you should be able to see evidence of that. You'll get the hang of it as you make changes and follow the alteration in the gaps.