Leaking fork seals is not a common occurance. Either the shop didn't install new seals or they damaged them.
I would take it back and ask them if they installed new seals (which they should have), or ask them to replair the problem.
It's possible they forks were overfilled and no longer leaking or there isn't anymore oil to leak out. Either way, the oil leak should be repaired and the correct amount of oil added.
Plumber's tape is not required on the threads as the threads don't actually seal anything, it's the seals that control the oil levels.