Frame 9E Gas Turbine Turning Gear Issue

Dear All,

We are encountering a problem that I didn't face before with Frame 9E, a power plant reported that Frame 9E unit couldn't achieve Turning Gear Operation
History of Events :
the unit was running on full load and the customer shut down the unit, the unit didn't go to Turning Gear operation the machine goes to 99 RPM speed and the turning gear motor started but it fail to increase the speed to 120 RPM and goes to zero speed in about 2 mins time.
The operation Team Tried again to start the crank motor and put the unit on turning gear in a time of 20 mins but without success.
The operation team found the Rubber coupling of the Turning gear motor damaged and they changed it.
the operation team left the unit for two days until the wheelspace temperature is below 67 Celsius and tried to put the unit again on turning gear but without success ( doors were closed but I'm not 100 % sure that the ventilation fans were stopped and the Lube oil pump was left running )
Hence. it was observed in the last attempt that Bearing Number 3 Temperature is a higher by the other bearings by 20 Celsius ( Temperature sensors on that bearing will be checked )

the Team checked several issues that can be the source of the problem.
1- checked the Lift oil pressure they confirm that the pressure is good 240 Bar, the flow control valves on the generator bearing were cleaned also
2- Torque converter Drain valve 20 TU was checked ( Reference and Feedback ) and was found to be in good condition.
3- performed a megger test on the Turning Gear motor ( 3 phases ) and the Readings are 9.9 G.OHM and 10.1 G.OHM and 11.2 G.OHM respectively
4- dismantle the Acc. shaft cover and Rotate the Rotor using a hydraulic Jack and a Ram and they report that the rotor rotated easily without any rubbing sounds observed.

Today we tried to operate the unit again and put on Turning Gear after more than 10 days the unit is stopped and just the lube oil system was running.
the Turbine Goes into 99 RPM speed and the turning gear motor started but the speed didn't increase and kept going down until 20 RPM and then it goes up and reached 119 rpm, and now the Turning Gear speed is going up and down.
Hence. when the speed of the turning Gear goes down, the temperature of bearing Number 3 is increasing and reach to alarm values, and when the speed increase more than 80 rpm it start to stabilize. ( we will check the probes for sure )

Note : unit was reported to run on high vibration after major inspection Bearing number 3 ( seismic vibration was reading 11 mm/sec ) before unit shut down, the vibration was analyzed before and was confirmed it's because a resonance in Exhaust casing causing the vibration to increase in bearing number 3 area ( bearing 2 and 4 are totally normal readings )

Thank you for your cooperation in advance.

Can you tell us if Control command/system of that Starting/cranking motor have been checked properly and operates acccording to the installed application code/program/software on the Turbine controller/governor

What is installed control system??

With more datas we can be better help and support and this case..