Fastlane lists the 124 boxes for $450-$550 depending on what your VIN# is, or you could try to get used. I needed a new one because mine was 'self tightening' so I pulled the one off my parts car and installed it.
My old box was dripping a few drops overnight & did not loose much noticable from the resevoir so the mechanic resealed it & never a problem since. Sounds like you had a catastrophic loss. If your mechanic cannot reseal a box properly he should not do them at all, sounds like your box was already screwed up from something else, or he doesn't know what he's doing and owe's you a freshly rebuilt box.