VERY low ime 912 ULS - leaking exhaust valve

Hello everybody,

Since we started our 912 ULS for the first time only one year ago, it has accumulated about 70 hours.

When we checked the compression today, we found cylinder #3 down to 73/87 psi with a noticeable hiss and air flow coming out of the exhaust. The other three cylinders had no measurable leakage

In retrospect, I am fairly certain that the leak has been existing for a while, maybe since the beginning, as one cylinder appeared to give less resistance during burping than the others.

When I borescoped it, I didn't see anything that stood out. I attached a few pictures.

For the last 40 or so hours, we have been running it on 100LL + Decalin.

What are your thoughts?

Oliver