TCs can start leaking from between the front & rear halves. As was mentioned, if it was just a drain & refill they most likely could not mess up anything that badly. If it was rebuilt, it's easy to mess up something.
..and yes, the only way to reseal your TC between the halves is splitting the case, cleaning it up really good, and then applying a bead of RTV (~1/8" thick bead around the whole front case half sealing surface; in circles around the bolt holes), reassembling the case, let it dry a couple hours before refilling.
1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...
1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***