You go, Dave!!  Lookin’ good.  (Hum-m-m; navy blue – what a surpriseJ).

No definite proof, but I am quite sure that it was due to excessive exhaust gas temps eventually melting away part of the inconel turbine blade and making the turbine unbalanced. I mostly flew around at peak EGT but now I will be more careful about keeping the EGT less than 1600. 

The melting point of inconel is up around 2500F.  Could the exhaust gas into the turbine ever get that high?  Peak EGT I see 2” from the port is about 1725F.  Do you measure the T.I.T.?

Another thought – it may be that at that temp the stress in the blades could cause a bit of visco-elastic creep over time which could put things out of balance.  (In a previous life I did a fair amount of finite element, visco-elastic stress analysis of high temperature metals.)

Al