2024-02-01 Valve Adjustment Bias Error?

Last March did a valve adjust. 

Later discovered slight oil leak from valve cover cap.

Removed cover. Thought I'd QC my work and re-measure clearances.

Sure as sh$t, 3 measure LOOSE. WTFO?

I was soo careful to follow the FSM to the letter. Checked and double-checked?

So what happened? How was this error introduced?

• ​Could it be that after 30 minutes of running, things 'settled' in to allow more clearance? Which led to this consideration.
• I routinely add engine oil to the bucket via a syringe. Is it possible that, in certain cases, the oil is 'trapped' in the bucket, creating a 'wedge' resulting in clearance reduction which in turn is increased by installing a thinner shim? Then, after some run time, the oil gets squished out, the clearance increase?

Just wondering about things on a rainy day...