May be something to do with this
"Following a recent engine failure, the BGA strongly recommends that whenever the valve clearances are checked or adjusted on the Grob G2500 engine, the engine is turned to fully open the valve and a check carried out to ensure there is clearance between the rocker arm and the valve roto cap. If you are affected, please pass this instruction on to your maintenance engineer."
That's all I know.
Cheers