my engine is just fully rebuilt with new ring valve seals and a secondhand turo from ebay with NO play at all( but seals could still be gone.

all compressions are equal , they all go to 10 bar after the third rotation of the engine.

In your case safechav i would say that the head gasket to oil way is leaking into your cylinder number 1. onlyway to find out is off with the head.

is the plug in cylinder 1 wet or oily??