Your PF configuration looks OK for a static egress, from a check by eyes and with no real remaining knowledge of the particulars of the PF syntax from nine years ago. (This is my way of politely saying I may not have any real clue if there is something else wrong with it.)
If revising the NAT rule for dynamic egress does not solve the problem, I would double check your IP forwarding sysctl, which is the only other thing I can think of.
If you wish to stay with -release 3.8, you might benefit from keeping a local copy of the OpenBSD Project webite as it existed when your OS was released:
$ cvs -d <pick your AnonCVS root> get -D 2005/11/02 www
or perhaps retain only the PF Users Guide web pages:
$ cvs -d <pick your AnonCVS root> get -D 2005/11/02 www/faq/pf