EGT's and CHT's run pretty close together..
Using 100LL and PHILLIPS 66 X/C 20W50..
Spark plugs indicate mixture on the rich side..
Did not perform a compression check so far..
The engine did not see any high power runs with cowling removed.
For certification I had to do a static thrust check on ground, but this was done with cowling on and CHT in view..
Today the cylinders were examined again with a high resolution/contrast borescope by a local A&P mechanic and an experienced forum member.
The bad news is they both agree that this is corrosion
The not so bad news, they both state its safe to fly, and check again in a few hours
Personally I find it hard to believe that a cylinder goes from shiny to corrosion in 3 months time while flying 25h..
On the other hand, there is also a chance that I loose weight. Its highly unlikely, but..