There are a lot of potential areas for leaks, especially with rear air. Those leak detecting dyes are not always visible either. There are probably 10+ o rings in the hard line connections that never get replaced.
If I had to do it again, I would delete the rear air, which alone will save you...
I unfortunately had to go down this road a few years ago. If the compressor truly did seize up, there is likely metal fragment contamination throughout the whole system. Even more fun with rear air. Ideally every component needs to be replaced and hard lines thoroughly flushed.
With a leak...