A/C: freon additives and the slow leak

No AC service tech in his right mind will touch a system that has sealer installed in it.

The fact that AC sealers exist on the market is in no way an endorsement that they don't cause problems, there is no shortage of people stupid enough to purchase such magic potions.

Please clarify the part about "a mechanic who wants to get more easy work," it seems to contradict the part where you say "the exchanger is buried in the dash, meaning lots of work to replace it.

No problem. I know it sounds contradictory, but I've done automotive work and know that wrestling with a transmission or other major work is a lot more strenuous than replacing some wiring, or piping or brake work. So, I consider this an easier task, save cataloging all the part placements. I've heard Click and Clack discussing using oil supplements for worn gaskets and rings when it's cost prohibitive to crack the manifold. I wondered if a similar situation carried into A/C systems.

Not really. Nothing is going to be more apparent to the customer than something amiss in their interior, a squeak, a rattle, god forbid a speck or smudge... Pulling a dash is awkward work, slightly cleaner than pulling a transmission, not many look forward to it.

Click and Clack is comedy (if you like that sort of comedy), nothing they say should be taken as accurate or advice.