I will always sniff between the seams of 2 adjoining pieces,pull back the armaflex sniff inside looking for any 'pool' of heavier than air refrigerent but only after checking the most obvious places.
A cpl of months ago had a leak that gave up it's 4 lbs in less than one day. Saturated soil from a leak under the slab of this 3 yr old condo. There where 4 line set entered into the chase pipe. Just digging around that chase pipe kept sending off my detector from the release of that pooled refrigerent.
Possible leak was from the braze joint at the first floor slab outlet for the second floor lines. Refrigerent filling the chase pipe and atmospheric conditions bringing it out to the outside end of the pipe?
The 2nd floor condo was empty for almost 3 yrs so AC was never used. Entering condo spiked my detector from the air handler drawing R22 gas from the chase wall into the living space. Isolating and nitro pressuring the individual coils and lines was the only way of finding the problem.