Now it's valves as well? Once more: boroscope inspections...
I see that Shell's into it as well,
here, e.g.:
Engines that have been involved with long, low power descents, or have taxied for some distance, can have quite low cylinder temperatures and this - as we now know - can lead to lead fouling. Again the advice from Textron Lycoming and Teledyne Continental Motors to remedy this is: once on the aircraft is on the stand, the engine speed should be kept between 1000 and 1200 rpm until the engine temperatures have stabilised.
I thought it was 1800 rpm. Anyway...
The 'remedy' quoted is based on intuition rather than real world data.
When I start my 360, if I sit at idle the engine gets warmer. Then it gets warmer. Then it gets hotter. Then it gets really hot. And, if I'm stupid enough to sit there idling or taxiing around without taking off, it will get even hotter and finally reach 'red line'. And, after I land and pull off the runway, the engine gets slowly hotter and hotter and hotter and...