When is it leaking?
When running and water is dripping out of ceiling grill
OR anytime and it's raining outside?
There is no caulking used...........or shouldn't be ever!!
There is a roof gasket that seals the roof opening.
If the 4 corner bolts are loose water can leak inside.
IF you snug up to much on bolts then gasket can be over compressed/warped and water can leak inside.
Roof gasket is 1" thick when new and should be compressed to only about 1/2 of thickness.
To access the 4 corner hold down bolts you have to remove the complete ceiling grill.
Then just snug up on the bolts slightly.
If evap coil drip pan drain holes are blocked (either debris or from over compressed roof gasket) condensation will get carried over via fan blower into discharge plenum and drip out of ceiling grill when A/C unit shuts down.