Coolant Separator Case Leak?

Had some work done on my truck last year to fix a giant coolant leak that had been building under the intake. They replaced my intake manifold and the gaskets in that area as well.

But I still had a slight coolant leak. Took it into a shop last week and they diagnosed it as an issue with the coolant separator case. They replaced it but wouldn't this have been noticed when working on that area previously? Shop said they fixed the engine valley silicone issue that is typical on these engines during last year's work but if that was the case why did they need to replace the separator case a year after? I don't know enough to know any better but my concern is that they missed the main issue last time or they simply didn't reseal the silicone properly and I just paid for almost the same issue twice. They did give me a slight bump off labor as an apology for having to pay for work in the same spot again. My guess is that they didn't inspect the EV/separator case last time and just resealed it but there was an issue near the seal area that continued to leak afterwards.

The shop does good work for a reasonable price but I am wondering if they are taking less responsibility than they should for this additional repair or if I am just tripping.

Appreciate any info