Have a look at your start technique. The trailing edge of the stage 1 nozzle hates long cool starts.
Also, have a look at your fuel nozzle condition, maybe even bringing the nozzle clean down to every 100 hour.
A point to remember, the M250 turbine temperature is measured between the stage 2 and 3 wheel, so the temp at the stage 1 nozzle will be a lot higher than you see on the gauge.