Looking for suggestions in which direction to go with this. Back story is I did a coolant flush a week ago and noticed infrequent bubbles from radiator after bleed. I’m at 200k miles now with no misfire, no CEL, no white smoke or sweet smell. No loss of coolant and engine essentially runs flawless at this point. I want to catch a potential problem before I overheat it and warp a head or burn out a valve.

I went for a leak down test and cylinder 1 is 18% and 2 is 20%, all others are 15%.

The tech didn’t note where the leak might be from but said it’s “in spec” and said head gasket looks good. I’m following up with them to get more info on their findings since they didn’t note any other details about leak.