Yes needs a replacement spring as proven. As said earlier, contact Darren Dawes for replacement spring _ worth a try:
Not surprised that you have high cruise boost (14-15psi), vanes are most likely nearly closed all the time, yes lower EGTs at the expense of high exhaust manifold pressures and reduced air flow rate (grams/sec). Worth checking that the actuator lever is still just resting against stop after adjusting.Darren Dawes had a replacement spring for the early Brass Dawes boost controller. Send him an email and he may send you one for elimination purposes (explain the boost situation briefly) _ info@3BarRacing.com
Also worth improving your air intake in time to let it breathe easier, this will bring cruise boost down as well. Aim for a nom 12psi cruise boost.
Do check your intercooler as it most likely does leaks.
Be interesting to hear how she goes with a serviceable boost controller. Room for improvement yet though.